TnE  International  Scientific  Series, 
vol.  XI. 


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THE    INTERNATIONAL    SCIENTIFIC  SERIES. 


ANIMAL  MECHANISM : 


A  TREATISE  ON 


TERRESTRIAL  AND  AERIAL  LOCOMOTION. 


BY 

E.  J.  MA]|fY. 

PROFESSOR  AT  THE  COLLEGE  OF  FRANCE,  AND  MEMBER  OF  TITR 
ACADEMY  OF  MEDICINE. 


WITH  ONE  IIUNDRED  AND  SEVENTEEN  ILLUSTRATIONS,  DRAWN  AND  ENGRAVED  UNDER 
TIIE  DIRECTION  OF  THE  AUTHOR. 


NEW  YORK: 
D.    APPLETON   AND  COMPANY, 

1,  3,  and  5  BOND  STREET. 
1890. 


TABLE  OF  CONTENTS. 


PAGE 

INTRODUCTION  1 


BOOK  THE  FIRST. 

FORCES  AND  ORGANS. 


CHAPTER  I. 

OF  FORCES  IN  THE  INORGANIC  KINGDOM  AND  AMONG 
ORGANISED  BEINGS. 

Matter  reveals  itself  by  its  properties— When  matter  acts,  we  con- 
clude that  forces  exist  —  Multiplicity  of  the  forces  formerly 
admitted  ;  tendency  to  their  reduction  to  one  force  in  the  inor- 
ganic kingdom — Indestructibility  of  force  ;  its  transformations 
— Vital  forces,  their  multiplicity  according  to  the  ancient 
physiologists  —  Several  vital  forces  are  reduced  to  physical 
forces— Of  laws  in  physics  and  in  physiology — General  theory 
of  physical  forces  5 

CHAPTER  II. 

TRANSFORMATION  OF  PHYSICAL  FORCES. 

To  prove  the  indestructibility  of  forces,  we  must  know  how  to 
measure  them — Units  of  heat  and  of  mechanical  work — Ther- 
mo-dynamics — Measure  of  forces  in  living  beings — Successive 
phases  of  the  transformation  of  bodies  ;  successive  development 
of  force  under  this  influence— The vmo-dyuamics  applied  to 
living  beings  if  3 

CHAPTER  HI. 

ON  ANIMAL  HEAT. 

Origin  of  animal  heat— Lavoisier's  theory — The  perfecting  of  this 
theory— Estimates  of  the  forces  contained  in  aliment,  and  in 
the  secreted  products— Difficulty  of  these  estimates— The  force 


vi 


CONTENTS. 


yielded  by  alimentary  substances  is  transformed  partly  into  heat 
and  partly  into  work— Seat  of  combustion  in  the  organism— 
Heating  of  the  glands  and  muscles  during  their  functions— Seat 
of  calorification — Intervention  of  the  causes  of  cooling — Animal 
temperature— Automatic  regulator  of  animal  temperature  .       .  19 


CHAPTEE  IV. 
ANIMAL  MOTION. 
Motion  is  the  most  apparent  characteristic  of  life ;  it  acts  on 
solids,  liquids,  and  gases — Distinction  between  the  motions  of 
organic  and  animal  life — We  shall  treat  of  animal  motion  only 
— Structure  of  the  muscles — Undulating  appearance  of  the  still 
living  fibre— Muscular  wave— Shock  and  myography — Multi- 
plicity of  acts  of  contraction — Intensity  of  contraction  in  its 
relations  to  the  frequency  of  muscular  shocks — Characteristics 
of  fibre  at  different  points  of  the  body  27 


CHAPTER  V. 
CONTEACTION  AND  WORK  OF  THE  MUSCLES. 
The  function  of  the  nerve— Speed  of  the  nervous  agent— Measures 
of  time  in  physiology — Tetanus  and  muscular  contraction — 
Theory  of  contraction— Action  of  the  muscles  ....  41 

CHAPTER  VI. 

OF  ELECTRICITY  IN  ANIMALS. 
Electricity  is  produced  in  almost  all  organised  tissues — Electric  cur- 
rents of  the  muscles  and  the  nerves — Discharge  of  electric 
fishes ;  old  theories  ;  demonstration  of  the  electric  nature  of 
this  phenomenon— Analogies  between  the  discharge  of  electrical 
apparatus  and  the  shock  of  a  muscle — Electric  tetanus — Rapidity 
of  the  nervous  agent  in  the  electrical  nerves  of  the  torpedo  ; 
duration  of  its  discharge  49 

CHAPTER  VII. 

ANIMAL  MECHANISM. 
Of  the  forms  under  which  mechanical  work  presents  itself — Every 
machine  must  be  constructed  with  a  view  to  the  kind  of  work 
which  it  has  to  perform — Correspondence  of  the  form  of  muscle 
with  the  work  which  it  accomplishes — Theory  of  Borelli — 
Specific  force  of  muscles — Of  machines ;  they  only  change  the 


CONTENTS. 


vii 


PAGE 

form  of  work,  but  do  not  increase  its  quality— Necessity  of 
alternate  movements  in  living  motive  powers — Dynamical  energy 
of  animated  motors  59 


CHAPTER  VIII. 

HARMONY  BETWEEN  THE  ORGAN  AND  THE  FUNCTION. — 
DEVELOPMENT  HYPOTHESIS. 

Each  muscle  of  the  body  presents,  in  its  form,  a  perfect  harmony 
with  the  nature  of  the  acts  which  it  has  to  perform — A  similar 
muscle,  in  different  species  of  animals,  presents  differences  of 
form,  if  the  function  which  it  has  to  fulfil  in  these  different 
species  is  not  the  same — Variety  of  pectoral  muscles  in  birds, 
according  to  their  manner  of  flight— Variety  of  muscles  of  the 
thigh  in  mammals,  according  to  their  mode  of  locomotion — 
Was  this  harmony  pre-established  ?—  Development  hypothesis  — 
Lamarck  and  Darwin  69 


CHAPTER  IX. 

VARIABILITY  OF  THE  SKELETON. 

Reasons  which  have  caused  the  skeleton  to  be  considered  the  least 
variable  part  of  the  organism — Proofs  of  the  yielding  nature  of 
the  skeleton  during  life,  under  the  influence  of  the  slightest  pres- 
sure, when  long  continued — Origin  of  the  depressions  and  pro- 
jections which  are  observed  in  the  skeleton —Origin  of  the 
articular  surfaces — Function  rules  the  organ— Variability  of  the 
muscular  system '  85 


BOOK  THE  SECOND. 

FUNCTIONS:  TERRESTRIAL  LOCOMOTION. 


CHAPTER  I. 

OF  LOCOMOTION  IN  GENERAL. 

Ccnditions  common  to  all  kinds  of  locomotion— Borelli's  comparison 
—  Hypothesis  of  the  reaction  of  the  ground — Classification  of  the 
modes  of  locomotion,  according  to  the  nature  of  the  point  of 
resistance,  in  terrestrial,  aquatic,  and  aerial  locomotion — Of  the 


viii 


CONTENTS. 


partition  of  muscular  force  between  the  point  of  resistance  and 
the  mass  of  the  body — Production  of  useless  work  when  the  point 
of  resistance  is  movable  102 

CHAPTER  IL 

TERRESTRIAL  LOCOMOTION  (BIPEDS). 

Choice  of  certain  types  in  order  to  study  terrestrial  locomotions- 
Human  locomotion — Walking — Pressure  exerted  on  the  ground, 
its  duration  and  intensity — Re-actions  on  the  body  during 
walking— Graphic  method  of  studying  them — Vertical  oscilla- 
tions of  the  body — Horizontal  oscillations— Attempt  to  repre- 
sent the  trajectory  of  the  pubis — Forward  translation  of  the 
body— Inequalities  of  its  velocity  during  the  instants  of  a 
pace  110 

CHAPTER  III. 

THE  DIFFERENT  MODES  OF  PROGRESSION  USED  BY  MAN. 

Description  of  the  apparatus  for  the  purpose  of  studying  the  various 
modes  of  progression  used  by  man — Portable  registering  appara- 
tus—Experimental apparatus  for  vertical  reactions— Walking — 
Running— Gallop— Leaping  on  two  feet  and  hopping  on  one — 
Notation  of  these  various  methods— Definition  of  a  face  in  any 
of  these  kinds  of  locomotion — Synthetic  reproduction  of  the 
various  modes  of  progression  124 

CHAPTER  IV. 
QUADRUPEDAL  LOCOMOTION  STUDIED  IN  THE  HORSE. 
Insufficiency  of  the  senses  for  the  analysis  of  the  paces  of  the  horse 
— Comparison  of  Duges— Rhythms  of  the  paces  studied  by  means 
of  the  ear — Insufficiency  of  language  to  express  these  rhythms 
— Musical  notation — Notation  of  the  amble,  of  the  walking  pace, 
of  the  trot — Synoptical  table  of  paces  noted  according  to  the 
definition  of  each  of  them  by  different  authors— Instruments 
intended  to  determine  by  the  graphic  method  the  rhythms  of  the 
various  paces,  and  the  re-actions  which  accompany  them    .  .138 

CHAPTER  V. 

EXPERIMENTS  ON  THE  PACES  OF  THE  HORSE. 
Double  aim  of  these  experiments  ;  determination  of  the  movements 
under  the  physiological  point  of  view,  and  of  the  attitudes  with 


f 


CONTENTS. 


PAGE 

reference  to  art— Experiments  on  the  trot — Tracings  of  the 
pressures  of  the  feet  and  of  the  re-actions — Notation  of  the  trot 
-—Piste  of  the  trot— Representation  of  the  trotting  horse— Ex- 
periments on  the  walking  pace— Notation  of  this  kind  of  motion  ; 
its  varieties — Piste  of  the  walking  pace — Representation  of  a 
pacing  horse  151 

CHAPTER  VI. 
EXPERIMENTS  ON  THE  PACES  OF  THE  HORSE. 
{Continued.*) 

Experiments  on  the  gallop— Notation  of  the  gallop— Re-actions — 
Bases  of  support — Piste  of  the  gallop— Representation  of  a 
galloping  horse  in  the  various  times  of  this  pace — Transition,  or 
passage,  from  one  step  to  the  other — Analysis  of  the  paces  by- 
means  of  the  notation  rule— Synthetic  reproduction  of  the 
different  paces  of  the  horse— Modes  of  walking  of  various 
quadrupeds  164 


BOOK  THE  THIRD. 

AERIAL  LOCOMOTION. 


CHAPTER  L 

OF  THE  FLIGHT  OF  INSECTS. 

Frequency  of  the  strokes  of  the  wing  of  insects  during  flight ;  acoustic 
determination ;  graphic  determination — Influences  which  modify 
the  frequency  of  the  movements  of  the  wing — Synchronism  of 
the  action  of  the  two  wings — Optical  determination  of  the  move- 
ments of  the  wing  ;  its  trajectory  ;  changes  in  the  plane  of 
the  wing;  direction  of  the  movement  of  the  wing    .       .       .  180 

CHAPTER  II. 

MECHANISM  OF  THE  FLIGHT  OF  INSECTS. 
Causes  of  the  movements  of  the  wings  of  insects — The  muscles  only 
give  a  motion  to  and  fro,  the  resistance  of  the  air  modifies  the 
course  of  the  wing — Artificial  representation  of  the  movements 
of  the  insect's  wing— Of  the  propulsive  effect  of  the  wings  of 


X 


CONTENTS. 


PAGE 

insects — Construction  of  an  artificial  insect  which  moves  hori- 
zontally—Change  of  plane  in  flight  196 

CHAPTER  III. 
OF  THE  FLIGHT  OF  BIRDS. 
Con  formation  of  the  bird  with  reference  to  flight— Structure  of  the 
wing,  its  curves,  its  muscular  apparatus— Muscular  force  of  the 
bird,  rapidity  of  contraction  of  its  muscles — Form  of  the  bird  ; 
stable  equilibrium,  conditions  favourable  to  change  of  plane- 
Proportion  of  the  surface  of  the  wings  to  the  weight  of  the  body 
in  birds  of  different  size  209 

CHAPTER  IV. 

OF  THE  MOVEMENTS  OF  THE  WING  OF  THE  BIRD 
DURING  FLIGHT. 
Frequency  of  the  movements  of  the  wing — Relative  durations  of  its 
rise  and  fall — Electrical  determination— My ographical  determi- 
nation— Trajectory  of  the  bird's  wing  during  flight— Construc- 
tion of  the  instruments  which  register  this  movement — Experi- 
ment—Elliptical figure  of  'the  trajectory  of  the  point  of  the 
wiug  226 

CHAPTER  V. 

OF  THE  CHANGES  IN  THE  PLANE  OF  THE  BIRD'S  WING 
AT  DIFFERENT  POINTS  IN  ITS  COUKSE. 
New  determination  of  the  trajectory  of  the  wing — Description  of 
apparatus — Transmission  of  a  movement  by  the  traction  of  a 
thread — Instrument  and  apparatus  to  suspend  the  bird — Experi- 
ment on  the  flight  of  a  pigeon — Analysis  of  the  curves— 
Description  of  the  apparatus  intended  to  give  indications  of  the 
changes  in  the  plane  of  the  wing  during  flight — Relation  of 
these  changes  of  plane  to  the  other  movements  of  the  wing      .  244 

CHAPTER  VI. 
RE- ACTIONS  OF  THE  MOVEMENTS  OF  THE  WING  ON 
THE  BODY  OF  THE  BIRD. 
Re-actions  of  the  movements  of  the  wing — Vertical  re-actions  in 
different  species  ;  horizontal  re-actions  or  changes  in  the 
rapidity  of  flight ;  simultaneous  study  of  the  two  orders  of 
re-actions — Theory  of  the  flight  of  the  bird — Passive  and  active 
parts  of  the  wing— Reproduction  of  the  mechanism  of  the  flight 
of  the  bird  264 


LIST  OF  ILLUSTRATIONS. 


APPARATUS  FOR  EXPERIMENTING  ON  MOVEMENT. 

PAGK 

F13.     2. — Theoretical  representation  of  myograph      .       .       .    .  31 

Fig.     3. — Marey's  myograph  32 

Fig.     7. — Arrangement  of  a  muscular  bundle  between  two  myo- 

graphical  clips  37 

Fig.    19. —Experimental  shoe,  intended  to  show  the  pressure  of  the 

foot  on  the  ground,  with  its  duration  and  its  phases      .  113 

Fig.   42. — Experimental  apparatus  to  show  the  pressure  of  the 

horse's  hoof  on  the  ground  148 

Fig.    43. — Apparatus  to  give  the  signals  of  the  pressure  and  rise  of 

the  horse's  hoof  .       .        .       .        .       .       .  .149 

Fig.   26. — Apparatus  to  determine  the  speed  of  walking  at  every 

instant  122 

Fig.    27. — Runner  provided  with  the  apparatus  intended  to  register 

his  different  paces  126 

Fig.    28.— Instrument  to  register  the  vertical  re-actions  during  the 

various  paces  127 

Fig.    44.— Figure  to  represent  a  trotting  horse,  furnished  with 
the  different  experimental  instruments ;  the  horseman 
carrying  the  register  of  the  pace.    On  the  withers  aud 
-  the  croup  are  instruments  to  show  the  re-actions  .  .150 

Fig.    93. — Apparatus  for  the  purpose  of  experimenting  on  the  con- 
traction of  the  thoracic  muscles  of  the  bird      .       .    .  229 

Fig.    99. — Buzzard  Hying,  with  the  apparatus  for  giving  signals  of 

the  movements  of  the  extremity  of  its  wing         .       .  241 

Fig.  103. — General  arrangement  of  the  recording  instrument;  apigeon 

attached  to  it,  and  conveying  signals       .       .       .    .  248 

Fig.  104. — Suspension  of  the  bird  in  the  apparatus  ....  250 

Fig.  109. — Apparatus  to  examine  tho  movements  of  the  wing,  aud 

the  changes  in  its  plane  260 

Fig.    21. — Transmission  of  an  oscillatory  movement  to  the  regis- 
tering apparatus  116 


xii 


LIST  OF  ILLUSTRATIONS. 


PAGE 

Fig.   24. — Showing  two  successive  positions  of  the  arm  of  the  instru- 
ment, and  the  corresponding  positions  of  the  tracing 

points  of  the  levers   .    .  120 

Fig.  98. — Elastic  point,  tracing  on  a  piece  of  smoked  glass  .  .  239 
Fig.  102. — Transmission  of  a  to-and-fro  movement  by  means  of  a 

simple  traction  thread  245 

ILLUSTRATIVE  APPARATUS. 

Fig.     1. — Showing  the  transformation  of  the  electricity  of  a  soil 

into  mechanical  work,  heat,  light,  and  chemical  action  .  10 
Fig.     6. — Appearance  presented  by  the  waves  in  a  muscular  fibre    .  36 
Fig.     9. — Transformation  of  heat  into  work  by  a  strip  of  india- 
rubber   39 


Of  the  Flight  of  Insects. 

Fig.   84. — Artificial  representation  of  the  movements  of  the  insect's 

wing  199 

Fig.  85. — Changes  in  the  plane  of  the  insect's  wing  .  ...  200 
Fig.- 87.— Artificial  insect,  to  illustrate  its  flight  ....  202 
Fig.   88. — Arrangement  of  the  artificial  insect,  so  as  to  obtain  the 

hovering  motion  or  the  ascending  flight   .       .       .    .  205 


Of  the  Hovering  of  the  Bird. 

Fig.  90.— Instrument  to  illustrate  the  hovering  of  the  bird  .  .217 

Fig.    91. — The  same,  explaining  the  upward  turn       .       •  .    .  218 

Fig.  92. —      „                          downward  ditto       .  .       .  219 


ANATOMY. 

Fig.  13.— Skeleton  of  a  flamingo  (after  Alph.  Milue-Ed wards ;  the 
wing  is  very  large,  the  sternum  very  short  and  deep, 
which  indicates  the  size  and  the  shortness  of  the  pectoral 
muscles  72 

Fig.    14.— Skeleton  of  a  penguin:  sternum  very  long,  wing  very 

short  73 

Fig.  15. — Skeleton  of  the  wing  and  sternum  of  the  sea  swallow 
(Hirundo  marina) ;  showing  the  extreme  shortness  of 
the  sternum,  and  the  great  length  of  the  wing .       .    .  74 

Fig.   89. — Different  curves  in  the  wing  of  the  bird  at  various  parts  of 

its  length  210 

Fig.  117. — Active  and  passive  parts  of  the  bird's  wing  .       .       .    .  276 

Fig.   83.— Structure  of  the  insect's  wing  196 


LIST  OF  ILLUSTRATIONS. 


xiii 


PAGE 

Fig.   16. — Muscles  of  the  thigh  in  man       .       .       .       .       .    .  76 

Fig.   17. — Muscles  of  the  thigh  of  the  magot  77 

Fig.   18.— Muscles  of  the  thigh  of  the  coaita  78 

DETERMINATIONS. 

Fig,  8. — Two  determinations  of  the  speed  of  the  muscular  wave  .  38 
Fig.  10. — Determination  of  the  speed  of  the  nervous  agent  in  man  .  43 
Fig.   12. — Measure  of  the  time  which  elapses  between  the  excitation 

of  the  electric  nerve,  and  the  discharge  of  the  torpedo  .  58 
Fig.    82. — Determination  of  the  direction  of  the  movements  in  an 

insect's  wing  195 

Fig.  94. — Experiment  to  determine  by  the  electric  and  myographic 
methods  at  the  same  time,  the  frequency  of  the  move- 
ments of  the  bird's  wing,  and  the  relative  duration  of 

its  elevation  and  depression  230 

Fig.    26. — Determination  of  the  rapidity  of  walking  at  various 

instants,  by  means  of  a  chronographic  tuning-fork       .  122 


NOTATIONS. 

Fig.  34. — Notation  of  a  tracing  of  man's  mode  of  walking  .  .  133 
FlG.   35. — Synoptical  notation  of  the  four  kinds  of  progression  used 

by  man  134 

Fig.   36. — Notations  of  the  gallop  (man)  134 

Fig.    37. — (Upper  line)  notation  of  a  series  of  jumps  on  two  feet. 

(Lower  line)  notation  of  hops  on  right  foot      .       .    .  135 

Notations  of  the  Paces  of  the  Horse. 

Fig.   38. — Notation  of  a  horse's  amble  142 

Fig.   39. — Notation  of  the  horse's  walking  pace  143 

FlG.   51. — Notation  of  the  walking  pace,  with  predominance  of  the 

lateral  pressures  .  ICO 

Fig.   45.— Graphic  curves  and  notation  of  the  horse's  trot   .       .    .  153 

FlG.   40. — Notation  of  a  horse's  trot   144 

Fig.   46.— Notation  of  the  irregular  trot  K>6 

FlG.    41. —  Synoptical  notations  of  the  paces  of  the  horse,  according 
to  various  writers. 
No.  1.    Amble,  according  to  all  writers. 
^     9  (  Broken  amble,  according  to  Merche. 
*    '  (  High  steps,  according  to  Bouley. 

! Ordinary  step  of  a  pacing  horso,  according  to  Magure. 
Broken  amble,  according  to  Bouley. 
Traquenade,  according  to  Lecoq. 


xiv 


LIST  OF  ILLUSTRATIONS. 


PAGB 

No.  4.    Normal  walking  pace,  according  to  Lecoq. 

No.  5.    Normal  walking  pace  (Boulejr,  Vincent  and  Goiffon 

Solleysel,  Colin). 
No.  6.    Normal  walking  pace,  according  to  Raabe. 
No.  7.    Disconnected  trot  (trot  de  coursier). 
No.  8.    Ordinary  trot.    (In  the  figure,  it  is  supposed  that  the 

animal  trots  without  leaving  the  ground,  which  occurs  but 

rarely.     The  notation  only  takes  into  account  the  rhythm 

of  the  impacts  of  the  feet). 
No.  9.    Norman  pace,  from  Lecoq. 

No.  10.  Traquenade,  from  Merche  146 

Fig.   56.— Gallop  in  three-time  166 

Fig.   62. — Notation  of  the  gallop  in  four-time  170 

Fig.   63. — Notation  of  full  gallop  ;  re-actions  of  this  pace        •  .171 

Fig.   64. — Transition  from  the  walk  to  the  trot  174 

Fig.   65. — Transition  from  the  trot  to  the  walk      .      •       •  .174 

Fig.    66. — Transition  from  the  trot  to  the  gallop  174 

Fig.  67. — Transition  from  the  gallop  to  the  trot  ....  174 
Fig.  68. — Notation  rule,  to  represent  the  different  paces  .  .  .  175 
Fig.   69. — Notation  rule  forming  the  representation  of  the  gallop  in 

three-time  176 


PISTES  OR  FOOT  TRACES  OF  THE  HORSE'S  FEET. 

Fig.  52. — Piste  of  the  walking  pace,  after  Vincent  and  Goiffon  .  .162 
Fig.  53. — Piste  of  the  amble,  after  Vincent  and  Goiffon  .  .  .  162 
Fig.  47. — Piste  of  the  trot  according  to  Vincent  and  Goiffon  .  .  157 
Fig.  57. — Piste  of  the  short  gallop  in  three-time  ....  167 
Fig.   58. — Piste  of  Eclipse's  gallop,  from  Cornieu.    The  prints  of  the 

hind-feet  are  very  far  before  those  of  the  fore-feet     .  .167 


REPRESENTATION  OF  THE  HORSE  IN  ITS  VARIOUS  PACES. 

Fig.   54.— Representation  of  the  horse  at  a  walking  pace  .       .       .  163 
Fig.   48. — Horse  trotting  with  a  low  kind  of  pace       .       .       .    .  157 
Fig.   49. — Horse  at  full  trot.    The  dot  placed  in  the  notation  corre- 
sponds with  the  attitude  represented   .       .       .  .158 
Fig.  59. — Horse  galloping  in  the  first  time  (right  foot  advancing), 

the  left  foot  only  on  the  ground  168 

Fig.  60. — Horse  galloping  in  the  second  time  (right  foot  forward)  .  169 
Fig.   61. — Horse  galloping  in  the  third  time  (right  foot  forward)     .  169 


LIST  OF  ILLUSTRATIONS. 


XV 


PAGE 

TRACINGS. 
Tracings  of  the  Muscles. 

Fio.     4.— Character  of  the  shock  according  to  the  degree  of  fatigue 

of  the  muscle  34 

Fig.  5. — Successive  transformations  of  the  shock  of  a  muscle  be- 
coming gradually  poisoned  by  veratrine.  Underneath 
and  on  the  left  of  the  figure  are  shown  the  first  effects 
of  the  poison  35 

Fio.   11. — Gradual  coalescence  of  the  shocks  produced  by  electric 

excitations  of  increasing  frequency  46 


Tracings  op  Human  Locomotion. 

Fig.   20. — Tracings  of  the  impact  and  the  pressure  of  the  two  feet  in 

our  ordinary  walk  114 

Fig.   22.— Tracings  of  the  oscillations  of  the  body  during  walking    .  117 
Fig.   25. — Tracing  of  the  impact  and  rise  of  the  right  foot,  furnished 
by  a  lever  subjected  at  the  same  time  to  10  vibrations 

per  second   .    .  121 

Fig.   29.— Tracing  produced  by  walking  upstairs     .       .       .  .128 
Fig.   30. — Tracing  produced  by  running  (in  man)       .       .       .    .  128 
Fig.    31. — Man  galloping  (right  foot  foremost).    Step-curves  and  re- 
actions.  There  is  an  encroachment  of  one  curve  over  the 
other,  and  then  a  suspension  of  the  body     .       .  .131 
Fig.   33. — Series  of  hops  on  the  right  foot.    The  duration  of  the 
time  of  suspension  remains  evidently  constant,  even 
when  that  of  the  pressure  of  the  foot  varies      .       .    .  132 
Fig.   32. — Leap  on  two  feet  at  once  131 


Tracings  of  tiie  Locomotion  of  the  Horse. 

Fig.   50. — Tracing  and  notation  of  the  walking  pace,  with  equal 

pressures  of  the  feet,  both  diagonally  and  laterally   .    .  160 

Fig.    45. — Tracing  and  notation  of  the  trot   153 

Fig.   55. — Tracing  and  notation  of  the  gallop  in  three-time  .       .    .  165 


Tracings  of  the  Flight  of  Insects. 

Fig.    70. — Showing  the  frequency  of  the  strokes  of  the  wing  of  a 

drone-fly  and  a  bee  183 

Fig.    72.— Graphic  tracing  of  the  middle  portion  of  the  course  of  a 

bee's  wing  189 


xvi 


LIST  OF  ILLUSTRATIONS. 


PAGE 

Fig.   73.— Tracing  of  the  middle  zone  of  a  humming-bird  moth.      .  190 

Fig.    74. — Tracing  of  the  course  of  a  wasps  wing  showing  the  upper 

part  of  the  curve  190 

Fig.   75. — Tracing  of  the  course  of  a  wasp's  wing  :  lower  loops     .  191 

Fig.   77. — Tracing  obtained  from  a  bee's  wing  in  a  plane  tangential 

to  the  cylinder  192 

Fig.  78  and  79. — Tracing  of  a  wasp's  wing,  compared  with  a  "Wheat- 
stone's  rod  192,  193 

Fig.    80. — Tracing  of  the  wing  of  a  humming-bird  moth  (lower 

border)  193 

Fig.    81. — Tracing  of  the  wing  of  a  tired  humming-bird  moth  .       .  194 

Tracings  of  the  Flight  of  Birds. 

Fig.    95. — Myographical  tracing  to  determine  the  frequency  of  the 

strokes  of  the  wing  in  different  species  .  .  .  .  232 
Fig.    96.— Differences  of  frequency  and  of  amplitude  in  the  strokes 

of  a  pigeon's  wing  234 

Fig.  105.  — Tracing  of  different  movements  of  the  pigeon's  wing  .  .  253 
Fig.  106-107. — Construction  of  the  trajectory  of  a  pigeon's  wing,  254,  255 
Fig.  110.— Simultaneous  tracing  of  the  different  movements  of  a 

buzzard's  wing  262 

Fig.  111. — Inclination  of  the  plane  of  the  wing,  with  reference  to  the 

axis  of  the  body  during  flight  263 

Fig.  113. — "Vertical  oscillations  of  the  bird  during  flight  .  .  .  266 
Fig.  114. — Relation  of  oscillations  with  muscular  acts  .  .  .  268 
Fig.  115. — Simultaneous  tracing  of  two  kinds  of  oscillation  in  the 

buzzard  271 

TRAJECTORIES. 

Fig.   23. — Attempt  to  illustrate,  by  means  of  a  metallic  wire,  the 

sinuous  trajectory  passed  through  by  the  pubis  .  .119 
Fig.   71. — Appearance  of  a  wasp  the  tips  of  whose  wings  have  been 

gilded  187 

Fig.    86. — Trajectory  of  an  insect's  wing  201. 

Fig.  100. — Elliptical  course  of  the  point  of  a  bird's  wing  .  .  .  242 
Fig.    76. — Tracing  of  a  vibrating  Wheatstone's  rod  ....  191 

Fig.   79.— Do.  tipped  with  a  wasp's  wing  193 

Fig.  101. — Ellipse  traced  by  a  Wheatstone's  red  on  a  revolving 

cylinder  .243 


ANIMAL  MECHANISM: 


TERRESTRIAL  AND  AERIAL  LOCOMOTION. 


INTRODUCTION. 

Living  beings  have  been  frequently  and  in  every  age 
compared  to  machines,  but  it  is  only  in  the  present  day 
that  the  bearing  and  the  justice  of  this  comparison  are  fully 
comprehensible. 

No  doubt,  the  physiologists  of  old  discerned  levers,  pulleys, 
cordage,  pumps,  and  valves  in  the  animal  organism,  as  in  the 
machine.  The  working  of  all  this  machinery  is  called  Animal 
Mechanics  in  a  great  number  of  standard  treatises.  But  these 
passive  organs  have  need  of  a  motor ;  it  is  life,  it  was  said, 
which  set  all  these  mechanisms  going,  and  it  was  believed 
that  thus  there  was  authoritatively  established  an  inviolable 
barrier  between  inanimate  and  animate  machines. 

In  our  time  it  is  at  least  necessary  to  seek  another  basis 
for  such  distinctions,  because  modern  engineers  have  created 
machines  which  are  much  more  legitimately  to  be  compared 
to  animated  motors ;  which,  in  fact,  by  means  of  a  little  com- 
bustible matter  which  they  consume,  supply  the  force  requisite 
to  animate  a  series  of  organs,  and  to  make  them  execute  the 
most  various  operations. 

The  comparison  of  animals  with  machines  is  not  onty  legiti- 
mate, it  is  also  extremely  useful  from  different  points  of  view. 
It  furnishes  a  valuable  means  of  making  the  mechanical 
phenomena  which  occur  in  living  beings  understood,  by 
placing  them  beside  the  similar  but  less  generally  known 
phenomena,  which  are  evident  in   the  action  of  ordinary 


2 


ANIMAL  MECHANISM. 


machines.  In  the  course  of  this  book,  we  shall  frequently 
borrow  from  pure  mechanics  the  synthetical  demonstrations 
of  the  phenomena  of  animal  life.  The  mechanician,  in  his 
turn,  may  derive  useful  notions  from  the  study  of  nature, 
which  will  often  show  him  how  the  most  complicated  problems 
may  be  solved  with  admirable  simplicity. 

Animal  mechanics  is  a  wide  field  for  exploration.  To 
every  function,  so  to  speak,  a  special  machinery  is  attached. 
The  circulation  of  the  blood,  the  respiration,  &c,  may  and 
ought  to  be  treated  separately,  so  that  we  shall  limit  this  work 
to  the  study  of  one  single,  essentially  mechanical,  function, 
locomotion  in  the  various  animals. 

It  is  easy  to  demonstrate  the  importance  of  such  a  subject  as 
locomotion,  which,  under  its  different  forms,  terrestrial,  aquatic, 
and  aerial,  has  constantly  excited  interest.  Whether  man  has 
endeavoured  to  utilize  to  the  utmost  his  own  motive  power, 
and  that  of  the  animals;  whether  he  has  sought  to  extend 
his  domain,  to  open  a  way  for  himself  in  the  seas,  or  to  rise 
into  the  air,  it  is  always  from  nature  that  he  has  drawn  his 
inspirations.  We  may  hope  that  a  deeper  knowledge  of  the 
different  modes  of  animal  locomotion  will  be  a  point  of 
departure  for  fresh  investigations,  whence  fuither  progress 
will  result. 

Every  scientific  research  has  a  powerful  attraction  in  itself ; 
the  hope  of  reaching  the  truth  suffices  to  sustain  those  who 
pursue  it,  through  all  their  efforts  ;  the  contemplation  of  the 
laws  of  nature  has  been  a  great  and  noble  source  of  enjoy- 
ment to  those  who  have  discovered  them*  But  to  humanity, 
science  is  only  the  means,  progress  is  the  aim.  If  we  can 
show  that  a  study  may  lead  to  some  useful  application,  we 
may  induce  many  to  pursue  it,  who  would  otherwise  merely 
follow  it  from  afar,  with  the  interest  of  curiosity  only. 
Without  pretending  to  recapitulate  here  all  that  has  been 
gained  by  the  study  of  nature,  we  shall  endeavour  to  set 
forth  what  may  be  gained  by  studying  it  still  further,  and 
with  more  care. 

Terrestrial  locomotion,  that  of  man,  and  of  the  great  mam- 
mals, for  instance,  is  very  imperfectly  understood  as  yet.  If 
we  knew  under  what  conditions  the  maximum  of  speed,  force, 


INTRODUCTION. 


8 


or  labour  which  the  living  being  can  furnish,  may  be  obtained, 
it  would  put  an  end  to  much  discussion,  and  a  great  deal  of 
conjecture,  which  is  to  be  regretted.  A  generation  of  men 
would  not  be  condemned  to  certain  military  exercises  which 
will  be  hereafter  rejected  as  useless  and  ridiculous.  One 
country  would  not  crush  its  soldiers  under  an  enormous 
load,  while  another  considers  that  the  best  plan  is  to  give 
them  nothing  to  carry.  We  should  know  exactly  at  what 
pace  an  animal  does  the  best  service,  whether  he  be  required 
for  speed,  or  for  drawing  loads  ;  and  we  should  know  what 
are  the  conditions  of  draught  best  adapted  to  the  utilization 
of  the  strength  of  animals. 

It  is  in  this  sense  that  progress  is  being  made  ;  but  if  we 
complain  with  reason  of  its  slow  advance,  we  must  only 
blame  our  imperfect  notion  of  the  mechanism  of  locomotion. 
Let  this  study  be  perfected,  and  then  useful  applications  of  it 
will  soon  ensue. 

Man  has  been  manifestly  inspired  by  nature  in  the  con- 
struction of  the  machinery  of  navigation.  If  the  hull  of 
the  ship  is,  as  it  has  been  justly  described,  formed  on  the 
model  of  the  aquatic  fowl,  if  the  sail  has  been  copied  from  the 
wing  of  the  swan  inflated  by  the  wind,  and  the  oar  from  its 
webbed  foot  as  it  strikes  the  water,  these  are  but  a  small  part 
of  nature's  loans  to  art.  More  than  two  hundred  years  ago, 
Borelli,  studying  the  stability  and  displacement  of  fish,  traced 
the  plan  of  a  diving-ship  constructed  upon  the  same  principle 
as  the  formidable  Monitors  which  made  their  appearance  in 
the  recent  American  war. 

In  modem  navigation  the  dynamic  question  still  leaves 
several  points  in  obscurity.  What  form  should  be  given  to  a 
ship  so  as  to  secure  its  meeting  with  the  least  possible  resist- 
ance in  the  water?  What  propeller  should  be  chosen  in 
order  to  utilize  the  force  of  the  machine  to  the  best  advan- 
tage ?  The  most  competent  men  in  such  matters  avow  that 
those  problems  are  too  complex  to  admit  of  the  conditions 
most  favourable  to  the  construction  of  ships  being  determined 
by  calculation.  Must  we  wait  until  empiricism,  by  dint  of 
ruinous  guesses,  shall  have  taught  us  how  a  problem  of 
which  nature   offers  us  such   diverse  solutions,  should  be 


4 


ANIMAL  MECHANISM. 


solved?  Ingenious  constructors  have  already  attempted  to 
imitate  the  natural  propellers  ;  they  have  fitted  up  small  boats 
with  machinery  which  works  like  the  tail  of  a  fish,  oscillating 
with  an  alternate  motion.  And  it  has  been  found  that  this 
apparatus,  although  still  imperfect,  already  constitutes  a 
powerful  propeller,  which  will  perhaps  be  preferred  hereafter 
to  all  those  which  have  hitherto  been  used. 

Aerial  locomotion  has  always  excited  the  strongest  curiosity 
among  mankind.  How  frequently  has  the  question  been 
raised,  whether  man  must  always  continue  to  envy  the  bird 
and  the  insect  their  wings ;  whether  he,  too,  may  not  one  day 
travel  through  the  air,  as  he  now  sails  across  the  ocean. 
Authorities  in  science  have  declared  at  different  periods,  as 
the  result  of  lengthy  calculations,  that  this  is  a  chimerical 
dream,  but  how  many  inventions  have  we  seen  realised  which 
have  also  been  pronounced  impossible.  The  truth  is,  that  all 
intervention  by  mathematics  is  premature,  so  long  as  the 
study  of  nature  and  experiment  have  not  furnished  the  precise 
data  which  alone  can  serve  as  a  sound  starting  point  for 
calculations  of  this  kind. 

We  shall  then  attempt  to  analyse  the  rapid  acts  which  are 
produced  in  the  flight  of  insects  and  of  birds ;  afterwards  we 
shall  endeavour  to  imitate  nature,  and  we  shall  see,  once 
more,  that  by  seeking  inspiration  from  her  we  have  the 
best  chance  of  solving  the  problems  which  she  has  solved. 

We  may  even  now  affirm,  that  in  the  mechanical  actions  of 
terrestrial,  aquatic,  and  aerial  locomotion,  there  is  nothing 
which  can  escape  the  methods  of  analysis  at  our  disposal. 
Would  it  be  impossible  for  us  to  reproduce  a  phenomenon 
which  we  understand?  We  will  not  carry  our  scepticism 
so  far. 

It  was  considered  for  a  long  time  that  chemistry,  all- 
powerful  when  it  was  a  question  of  decomposing  organic 
substances,  would  always  remain  incapable  of  reproducing 
them.    What  has  become  of  this  disheartening  prediction  ? 

We  hope  that  the  reader  who  follows  the  experimental 
researches  detailed  in  this  book  will  draw  from  them  this 
conviction,  that  many  of  the  impossibilities  of  the  present, 
need  only  a  little  time  and  much  effort  to  become  realities. 


BOOK  THE  FIEST. 


CHAPTER  I. 

FORCES  AND  ORGANS. 

Of  forces  in  the  inorganic  kingdom  and  among  organised  beings — Matter 
reveals  itself  by  its  properties— When  matter  acts,  we  conclude  that 
forces  exist— Multiplicity  of  forces  formerly  admitted;  tendency  to 
their  reduction  to  one  force  in  the  inorganic  kingdom — indestruc- 
tibility of  force  ;  its  transformations — Vital  forces,  their  multiplicity 
according  to  the  ancient  physiologists  —  Several  vital  forces  are 
reduced  to  physical  forces — Of  laws  in  physics  and  in  physiology — 
General  theory  of  physical  forces. 

We  know  matter  only  by  its  properties,  which  we  could  not 
conceive  of  apart  from  matter.  The  word  property  does  not 
answer  to  anything  real :  it  is  an  artifice  of  language  ;  thus,  the 
expressions,  weight,  heat,  hardness,  colour,  &c,  attributed  to 
various  bodies  in  nature,  mean  that  these  bodies  manifest 
themselves  to  our  senses  by  certain  effects  which  have  been 
made  known  to  us  by  daily  experience. 

When  matter  acts,  that  is  to  say,  when  it  changes  its  state, 
there  occurs  what  we  call  a  phenomenon,  and  by  a  new  appli- 
cation of  language  we  call  the  uuknown  cause  which  has 
produced  this  phenomenon,  Force.  A  body  which  falls,  a 
river  which  flows,  a  fire  which  warms  us,  the  lightning  which 
flashes,  two  bodies  which  combine,  &c,  all  these  correspond  to 
manifestations  of  forces  which  we  call  gravity,  mechanical 
force,  heat,  electricity,  light,  chemical  affinities,  &0. 

In  the  first  ages  of  science  the  number  of  forces  was  almost 
infinitely  multiplied.  Each  particular  phenomenon  was  re- 
garded as  the  manifestation  of  a  special  force.  But  by  degrees 
it  was  recognised  that  divers  manifestations  might  result  from 
3 


6 


ANIMAL  MECHANISM. 


a  single  cause ;  and  thenceforth  the  number  of  forces  which 
were  admitted  diminished  considerably. 

Weight  and  attraction  were  reduced  to  one  and  the  same 
force  by  Newton,  who  recognised,  in  the  falling  of  the  apple 
to  the  ground,  and  the  retention  of  the  star  in  its  orbit,  the 
effects  of  an  identical  cause — universal  gravitation.  Ampere 
reduced  magnetism  to  a  manifestation  of  electricity.  Light 
and  heat  have  long  since  been  regarded  as  manifestations  of  an 
identical  force,  an  extremely  rapid  vibratory  motion  imparted 
to  the  ether. 

In  our  own  time  a  grand  conception  has  arisen,  once  more 
to  change  the  face  of  science.  All  the  forces  of  nature  are 
reduced  to  one  only.  Force  may  assume  any  appearance  ;  it 
becomes,  by  turns,  heat,  mechanical  work,  electricity,  light ; 
it  gives  rise  to  chemical  combinations  or  decompositions. 
Occasionally,  force  seems  to  disappear,  but  it  has  only  hidden 
itself;  we  can  find  it  again  in  its  entirety,  and  make  it  pass 
anew  through  the  cycle  of  its  transformations. 

Force,  which  is  inseparable  from  matter,  is,  like  it,  inde- 
structible, and  to  both  the  absolute  principle,  that  in  nature 
nothing  is  created  and  nothing  is  destroyed,  is  applicable. 

Before  we  enter  upon  a  detailed  exposition  of  this  great 
conception  of  the  conservation  of  force  and  its  transformations 
in  the  inorganic  world,  let  us  see  whether  any  analogous 
generalisation  has  been  arrived  at  in  the  science  of  organised 
bodies. 

The  living  being,  in  its  manifestations  of  sensibility,  intelli- 
gence, and  spontaneity,  shows  itself  to  be  so  different  from 
the  inert  and  passive  bodies  of  inorganic  nature ;  the  genera- 
tion and  the  evolution  of  animals  are  so  peculiar  to  them- 
selves ;  that  the  earliest  observers  traced  an  absolute  boundary 
between  the  two  kingdoms  of  nature. 

Particular  forces  were  imagined,  to  which  each  of  the 
normal  phenomena  of  life  was  attributed,  while  others,  like 
malignant  genii,  presided  over  the  production  of  the  maladies 
by  which  everything  that  has  life  may  be  attacked. 

The  complexity  of  the  phenomena  of  life  hindered  observers 
for  a  long  time  from  discerning  the  link  which  united  them, 
and  prevented  their  referring  to  one  and  the  same  cause  these 


FORCES  AND  ORGANS. 


7 


manifold  effects,  and  thus  reducing  the  number  of  forces 
which  had  at  first  been  admitted.  Man  ended  by  taking 
the  fictions  of  his  imagination  for  realities.  Little  by  little, 
the  charm  of  the  unintelligible  exercising  fascination  over 
him,  he  at  last  denied  that  physical  laws  had  any  in- 
fluence upon  living  beings.  This  extravagant  mysticism 
represented  certain  animals  as  capable  of  withdrawing  them- 
selves from  the  influences  of  weight ;  according  to  it,  animal 
heat  was  of  another  essence  than  that  of  our  hearths  ;  subtle 
and  impalpable  spirits  circulated  in  the  vessels  and  the  nerves. 

Time  has  not  even  yet  disposed  of  all  these  absurdities; 
but  we  can  prove  that  the  science  of  life  tends  at  present 
to  undergo  a  transformation  as  complete  as  that  of  the  phy- 
sical sciences,  whose  development  we  have  just  sketched. 
Physiology,  guided  by  experience,  seeks  and  finds  the  physical 
forces  in  a  great  number  of  vital  phenomena ;  every  day  sees 
an  increase  in  the  number  of  cases  to  which  we  can  apply 
the  ordinary  laws  of  nature.  That  which  escapes  them 
remains  for  us  the  unknown,  but  no  longer  the  unknowable. 
Among  the  phenomena  of  life,  those  which  are  intelligible 
to  us  are  precisely  of  the  physical  or  mechanical  order. 

In  the  living  organism  we  shall  find  those  manifestations 
of  force  which  are  called  heat,  mechanical  action,  electricity, 
light,  chemical  action ;  we  shall  see  these  forces  transforming 
themselves  one  into  the  other,  but  we  must  not  hope  to  arrive 
immediately  at  the  numerical  determination  of  the  laws  which 
regulate  the  transformations  of  these  forces.  The  animal 
organism  does  not  lend  itself  to  exact  measurements,  its  com- 
plexity is  too  great  for  valuations,  to  which  physicists  attain 
with  great  difficulty  by  making  use  of  the  simplest  machines. 

Each  science,  according  to  its  degree  of  complexity,  is 
approaching  more  or  less  surely  to  the  mathematical  precision 
at  which  it  must  arrive  sooner  or  later.  A  law  is  only  the 
determination  of  numerical  relations  between  different  phe- 
nomena ;  there  is  then  no  perfect  physiological  law.  In  the 
phenomena  of  life  it  is  scarcely  possible  to  determine  and  to 
foresee  anything  except  the  manner  in  whicli  the  variation  will 
be  produced.  Hitherto,  the  physiologist  has  reached  only  that 
degree  of  knowledge  which  the  astronomer  would  possess,  who 


V 


8  ANIMAL  MECHANISM. 

knew,  for  instance,  that  the  attraction  between  two  heavenly 
bodies  diminishes  when  their  distance  increases,  but  who  had 
not  yet  determined  the  law  of  inverse  proportionality  to  the 
square  of  distances.  Or,  he  is  like  the  physicist  who  has  proved 
that  compressed  gases  diminish  in  volume,  but  who  has  not 
found  the  numerical  relation  between  their  volume  and  the 
pressure. 

Without  doubt,  however,  there  are  numerical  relations 
between  the  phenomena  of  life ;  and  we  shall  arrive  at  the 
discovery  of  them  more  or  less  speedily,  according  to  the 
exactitude  of  the  methods  of  investigation  to  which  we  have 
recourse. 

If  physicists  had  limited  themselves  to  establishing  that 
bodies  dilate  as  they  become  heated,  and  if  they  had  not 
sought  to  measure  the  temperature  of  those  bodies  and  the 
volume  which  they  assume  with  each  variation  of  the  temper- 
ature, they  would  have  had  only  an  imperfect  idea  of  the 
phenomena  of  the  dilatation  of  bodies  by  heat.  For  a  long 
time  physiologists  confined  themselves  to  pointing  out  that 
such  or  such  an  influence  augments  or  diminishes  the  force  of 
the  muscles,  causes  the  rapidity  of  their  motions  to  vary, 
increases  or  diminishes  sensibility  and  motive  power.  Science, 
in  our  time,  has  become  more  exacting,  and  already  the 
rigorous  determination  of  the  intensity  and  duration  of  certain 
acts,  of  the  form  of  different  movemeDts,  of  the  relations  of 
succession  between  two  or  several  phenomena,  the  precise 
estimation  of  the  rapidity  of  the  blood,  or  of  the  transference 
of  the  sensitive  or  motive  nervous  agent;  all  these  exact 
measures  introduced  into  physiology,  lead  us  to  hope  that 
from  more  scrupulous  measurement  better  formulated  laws 
will  soon  result. 

In  the  comparison  which  we  are  about  to  make  between 
the  physical  forces  and  those  which  animate  the  animal 
organism,  we  shall  take  it  for  granted  that  the  fundamental 
notions  recently  introduced  into  science,  and  by  which  all  those 
forces  tend  to  reduce  themselves  to  one  only,  that  which 
engenders  motion,  are  known;  and  shall,  therefore,  confine 
ourselves  to  a  rapid  sketch  of  the  new  theory. 

The  value  of  a  theory  depends  on  the  number  of  the  facts 


FORCES  AND  ORGANS. 


9 


which  it  embraces ;  that  of  the  unity  of  the  physical  forces 
tends  to  absorb  them  all.  From  the  invisible  atom  to  the  celes- 
tial body  lost  in  space,  everything  is  subject  to  motion.  Every- 
thing- gravitates  in  an  immense  or  in  an  infinitely  little  orbit. 
Kept  at  a  definite  distance  one  from  the  other,  in  proportion 
to  the  motion  which  animates  them,  the  molecules  present 
constant  relations,  which  they  lose  only  by  the  addition  or  the 
subtraction  of  a  certain  quantity  of  motion.  In  general, 
increase  of  motion  enlarges  the  orbit  of  the  molecules,  and 
widening  their  distance  from  each  other,  increases  the  volume 
of  the  bodies.  By  this  rule,  heat  is  proved  to  be  a 
source  of  motion.  Under  its  influence  the  molecules,  becom- 
ing more  and  more  separated,  cause  bodies  to  pass  from 
solid  to  liquid,  and  then  to  a  gaseous  state.  These 
gases  become  indefinitely  dilated  by  the  addition  of  fresh 
quantities  of  heat.  But  that  force  which  lends  extreme 
rapidity  to  the  motion  of  the  molecules,  that  force  which  is 
admitted  in  theory  is  rendered  tangible  by  experiment ;  its 
intensity  is  measured  by  opposing  to  the  dilatation  of  a  body 
an  obstacle  which  it  will  have  to  surmount.  Thus  it  is  that 
the  molecules  of  gases  or  vapours  imprisoned  in  the  cylinder 
of  machines,  communicate  to  the  partitions  and  to  the  piston 
the  pressure  which  is  employed  in  producing  action  by 
machinery.  This  mechanical  action  is,  in  its  turn,  trans- 
formed into  heat  if  the  conditions  of  the  experiment  be  re- 
versed ;  if,  for  example,  an  external  force,  thrusting  back 
the  piston  of  an  air-pump,  restrains  the  molecular  motions  by 
violent  compression. 

The  new  theory  has  thrown  light  upon  certain  hypotheses, 
those,  among  others,  which  claimed  admission  for  the  latent 
heat  of  fusion,  or  of  vaporisation  of  bodies,  the  latent  heat  of 
dilatation  of  gases.  It  has  suppressed  others  ;  for  instance, 
the  discovery  of  atmospheric  pressure  has  banished  the 
hypothesis  which  has  now  become  ridiculous,  that  nature 
abhors  a  vacuum. 

Although  the  theory  accommodates  itself  with  less  ease  to 
the  interpretations  of  luminous  and  electric  phenomena,  it 
admits,  according  to  the  great  analogy  between  these  phe- 
nomena and  heat,  of  supposing  that  they  themselves  are  o^y 


10 


ANIMAL  MECHANISM. 


manifestations  of  motion.  Besides,  the  transformation  of 
motion  into  heat,  into  electricity,  into  light,  may  be  proved 
experimentally. 

Fig.  1  represents  the  details  of  the  experiment. 


Fig.  1. — Showing  the  transformation  of  the  electricity  of  a  battery  into  mecha- 
nical action,  into  heat,  light,  and  chemical  action. 

Various  instruments  are  so  arranged  upon  a  table  that  an 
electric  current,  engendered  by  a  battery  P,  may  be  made  to 
pass  through  them.*4  The  current  is  conducted  in  an  elliptic 
circuit,  on  a  small  square  board,  represented  in  the  centre  of 
the  figure.  This  circuit  is  formed  of  a  thick  copper  wire ; 
at  certain  points  this  wire  is  interrupted  and  dipped  into 
cups  of  mercury,  from  which  other  wires  communicate  with 
the  various  apparatus  through  which  the  current  is  to  be  con- 
ducted. In  Fig.  1,  the  metallic  bridges  1,  2,  3,  4,  5,  connect 
the  cups  of  mercury,  and  form  a  complete  circuit,  which  the 
current  may  traverse  without  passing  through  the  various 
apparatus  placed  around  it. 

If  we  take  away  loop  No.  1,  the  current  which  passed 
through  that  loop  is  forced  to  traverse  the  elliptical  circuit 
without  passing  through  the  surrounding  apparatus.  But  if  we 

*  Instead  of  the  single  element  represented  in  the  Figure,  it  is  necessary 
to  employ  a  series  of  Bunsen's  cells,  to  realise  the  experiments  perfectly. 


FORCES  AND  ORGANS. 


11 


afterwards  remove  loop  No.  2,  the  current  must  traverse  the 
apparatus  M,  which  is  an  electro-magnetic  motor.  This  appa- 
ratus will  begin  to  move  and  will  produce  mechanical  action. 

Let  us  at  the  same  time  remove  loop  No.  3,  the  current 
must  also  traverse  a  registering  thermometer.  [That 
instrument  is  constructed  as  follows.  It  is  a  sort  of  Reiss' 
thermometer,  formed  of  a  spiral  of  platinum,  which  the  current 
traverses,  and  which  is  conducted  into  a  flask  full  of  air. 
Under  the  influence  of  the  heating  of  the  spiral  by  the  current 
which  traverses  it,  the  air  in  the  bottle  dilates,  and  passes, 
through  a  long  tube,  into  the  registering  apparatus.  The 
lr.tter  is  composed  of  a  drum  of  metal,  closed  on  the  upper 
side  by  a  membrane  of  india-rubber.  When  the  air  pene- 
trates into  the  drum,  the  membrane  swells,  and  lifts  up  a 
registering  lever,  which  traces  on  a  turning  cylinder  E,  a  curve 
whose  elevations  and  depressions  correspond  with  the  rise  and 
fall  of  the  temperature.] 

By  removing  loop  No.  4,  we  force  the  current  to  traverse 
an  apparatus  L,  with  carbon  points,  in  which  electricity 
gives  birth  to  the  bright  light  with  which  every  one  is 
acquainted.  When  it  passes  through  the  voltameter  V,  the 
current  produces  decomposition  of  the  water.  The  intensity 
of  the  current  is  measured  by  the  quantity  of  water  decom- 
posed, i.e.,  by  the  volumes  of  hydrogen  and  oxygen  which 
are  disengaged. 

We  see,  in  the  first  place,  by  means  of  this  apparatus, 
that  electricity  can  become  successively  mechanical  work  in  the 
motor  M,  heat  in  the  spiral  of  the  thermometer  T,  light 
between  the  carbon  points  L,  and  chemical  action  in  the 
voltameter  V. 

But  we  also  recognise  that  the  electricity  which  undergoes 
one  of  those  metamorphoses  is  taken  away  from  the  current 
whose  energy  is  thus  diminished.  If,  for  example,  we  make 
the  motor  M  work,  we  shall  see  that  the  register  marks  a 
diminution  of  heat  in  the  thermometer.  If  we  stop  the 
electro-magnetic  motor  with  the  hand,  an  increase  in  the 
temperature  becomes  immediately  apparent;  the  registered 
curve  rises. 

When  the  electro-magnetic  motor  is  working,  we  see  the 


L2 


ANIMAL  MECHANISM. 


intensity  of  the  light  diminish,  and  the  decomposition  of 
the  water  in  the  voltameter  grow  less.  All  these  phenomena 
resume  their  pristine  energy  as  soon  as  we  suppress  the 
production  of  mechanical  action. 

During  this  time,  all  the  force  expended  in  these  various 
forms  of  apparatus  is  disengaged  from  the  battery  under  the 
influence  of  a  chemical  action:  the  transformation  of  a  certain 
quantity  of  zinc  into  sulphate  of  zinc.  Thus,  in  the  furnace 
of  a  steam  engine,  the  combustion  of  the  coal,  that  is  to  say, 
the  oxidation  which  transforms  carbon  into  carbonic  acid 
disengages  heat,  which,  is  afterwards  converted  into  work. 

But  this  force,  disengaged  from  bodies,  was  contained  in 
them  when  the  zinc  was  in  the  condition  of  metal,  and  the 
carbon  in  the  state  of  coal;  these  bodies  had  employed  in 
their  formation  the  same  quantity  of  force  which  they 
have  yielded  up  in  passing  into  another  condition.  Thus  it 
would  be  necessary  to  restore  to  the  sulphate  of  zinc  and  to 
the  carbonic  acid  as  much  electricity  or  heat  as  they  have 
thrown  out,  in  order  to  reproduce  the  metallic  zinc  or  the 
carbon  in  a  pure  state. 

According  to  the  modern  theory,  force  which  manifests 
itself  at  a  given  moment  is  not  created,  but  only  rendered 
sensible,  from  being  latent. 

Here  in  tension  is  that  potential  force,  which,  stored  up  in 
a  body,  waits  the  opportunity  to  manifest  itself.  Thus  a 
stretched  spring  will  at  the  end  of  an  indefinite  time  give  back 
the  force  which  has  been  used  to  stretch  it ;  and  a  weight, 
lifted  to  a  certain  height,  will  restore,  the  instant  it  falls, 
the  work  that  has  been  employed  upon  raising  it. 


TRANSFORMATION  OF  PHYSICAL  FORCES.  13 


CHAPTER  H. 

TRANSFORMATION  OF  PHYSICAL  FORCES. 

I'o  prove  the  indestructibility  of  forces,  we  must  know  how  to  measure 
them — Units  of  heat  and  of  mechanical  work — Thermo-dynamics — 
Measure  of  forces  in  living  beings— Successive  phases  of  the  trans- 
formation of  bodies  ;  successive  throwing  off  of  force  under  this  influ- 
ence— Thermo-dynamics  applied  to  living  beings. 

We  have  just  seen  that  force,  in  the  different  states  which 
it  presents,  may  be  now  latent,  or  potential,  or  again  in  action, 
in  the  form  of  heat,  electricity,  or  mechanical  activity. 

To  follow  this  force  through  all  its  different  transformations, 
to  establish  that  no  portion  of  it  is  lost,  a  means  of  measuring 
it  under  all  its  forms  is  necessary.  The  chemist  can  prove 
the  indestructibility  of  matter,  by  showing,  with  a  balance, 
that  a  gramme  of  matter  will  preserve  its  weight  through  all 
the  changes  of  condition  that  can  be  imposed  upon  it.  Let 
that  matter  be  weighed  in  the  liquid  state,  in  the  solid  state, 
or  in  the  gaseous  state,  the  weight  of  a  gramme  will  always 
be  found  under  the  most  various  volumes  and  aspects. 

A  measure  is  then  necessary  for  the  different  manifestations 
of  force.  Every  quantity  of  heat,  of  electricit}',  or  of  mechani- 
cal work  ought  to  be  compared  with  a  particular  unit,  as  every 
weight  ought  to  be  compared  with  the  unit  of  weight. 

Unit  of  heat.  The  sensations  of  heat  and  cold  which  we 
experience  at  the  contact  of  different  bodies  do  not  correspond 
with  the  quantity  of  heat  which  those  bodies  contain.  Ther- 
mometrical  apparatus  are  not  in  a  condition  to  give  us  the 
measure  of  the  quantities  of  heat,  since  different  bodies, 
presenting  to  our  senses  and  by  the  thermometer  the  same 
temperature,  may  yield  very  unequal  quantities  of  heat.  But, 
to  warm  the  same  weight  of  a  body  to  the  same  number  of 
degrees,  the  same  quantity  of  heat  will  always  be  necessary. 

Now,  according  to  the  agreement  which  has  been  come  to 
in  France  and  in  many  other  countries,  the  unit  of  heat  or 


14 


ANIMAL  MECHANISM. 


calorie  is  the  quantity  of  heat  necessary  to  raise  a  kilogramme 
of  water  from  zero  to  one  degree  centigrade. 

Unit  of  work.  Mechanical  force  has  been  accurately  de- 
fined only  since  the  notion  of  work  has  been  introduced  into 
science.  The  unit  of  mechanical  work  admitted  in  France 
is  the  kilogrammetre ;  that  is  to  say,  the  force  necessary  to 
raise  the  unit  of  weight — the  kilogramme — to  the  unit  of 
height,  the  metre. 

Electric  force  is  measured  by  one  of  its  effects,  the  decom- 
position of  water,  for  it  is  demonstrated  that  to  decompose 
the  same  volume  of  water  the  same  quantity  of  electricity  will 
always  be  requisite. 

These  measures  of  forces  in  action  furnish,  in  their  turn, 
the  means  of  estimating  the  quantity  of  potential  force  con- 
tained in  a  body.  Thus,  it  will  be  demonstrated  that  in  a 
kilogramme  of  coal,  and  in  the  quantity  of  oxygen  necessary 
to  transform  that  coal  into  carbonic  acid,  there  were  in  tension 
7000  units  of  heat,  since  by  combining  all  the  heat  disen- 
gaged by  combustion,  a  mass  of  water  of  7000  kilogrammes 
shall  have  been  heated. 

But  a  substance  which  burns  is  not  always  completely 
oxidized ;  hence,  it  does  not  put  in  action  the  totality  of  the 
force  which  it  contained  in  tension.  A  kilogramme  of  carbon, 
for  example,  may  undergo  only  a  first  degree  of  oxidation,  and 
thus  becoming  oxide  of  carbon  it  yields  only  5000  units  of 
heat.  This  oxide  of  carbon  burning  in  its  turn,  and  becoming 
carbonic  acid,  will  then  yield  only  the  remaining  2000  units 
of  heat. 

Transformation  of  physical  forces  takes  place,  as  we  have 
said,  without  any  loss  of  the  transformed  force.  To  demon- 
strate this,  it  must  be  proved  that  a  certain  number  of  units 
of  heat  transformed  into  work,  will  furnish  a  constant  number 
of  kilogrammetres,  and  inversely,  that  this  work  in  becoming 
heat  again,  will  restore  the  primitive  number  of  units  of  heat. 

The  science  which  explains  the  relations  between  heat  and 
mechanical  work,  and  fixes  the  value  of  the  mechanical  equivalent 
of  heat  is  called  thermo- dynamics.  This  conception,  which  is 
the  complement  of  the  theory  of  the  transformation  of  forces, 
and  which  proves  that   in  their  transformation   they  lose 


TRANSFORMATION  OF  PHYSICAL  FORCES.  15 


nothing  of  their  value,  is  justly  considered  the  most  remarkable 
of  modern  times. 

Partly  seen  by  Sadi-Carnot,  clearly  formulated  by  R.  Mayer, 
demonstrated  brilliantly  by  the  experiments  of  Joule,  the 
notion  of  the  equivalence  of  forces  is  now  admitted  by  all 
physicists.  Each  day  furnishes  a  fresh  confirmation  of  this 
doctrine,  and  leads  to  greater  precision  in  the  determination  of 
the  mechanical  equivalent  of  heat.  The  value  now  generally 
admitted  for  that  equivalent  is  425,  that  is  to  say,  that  work 
equal  to  425  kilogrammetres  must  be  transformed  into  heat 
to  obtain  a  unit,  and  inversely,  that  the  heat  capable  of  heat- 
ing to  one  degree  one  kilogramme  of  water  at  zero,  if  it  be 
transformed  into  work,  can,  in  its  turn,  lift  a  weight  of  425 
kilogrammes  one  metre.* 

But  one  restriction  must  be  placed  upon  the  estimation 
of  thermo-dynamic  transformations.  Carnot  suspected,  and 
Clausius  had  clearly  established  that  in  the  case  of  heat  being 
employed  to  produce  work,  the  heat  cannot  transform  itself 
altogether,  and  that  the  greater  part  remains  still  in  the  state 
of  heat ;  while  in  the  inverse  operation  the  whole  of  the  work 
applied  to  that  effect  may  be  transformed  into  heat.  This 
does  not  exclude  the  law  of  equivalence,  of  which  we  have 
just  spoken ;  for  if  it  be  true  that,  in  a  steam  engine  for 
instance,  there  is  only  to  be  found  under  the  form  of  work  a 
email  quantity,  about  1 2°  of  the  heat  produced  by  the  fur- 
nace, it  is  no  less  true  that  the  quantity  of  heat  which  lias 
disappeared  furnishes  in  work  the  exact  number  of  kilo- 
grammetres which  corresponds  to  its  mechanical  equivalent. 

These  notions  had  no  sooner  been  introduced  into  science 
than  the  physiologists  endeavoured  to  use  them  for  the 
clearing  up  of  the  obscure  question  of  heat  and  work  pro- 
duced by  animals.  The  assimilation  of  living  beings  to 
thermal  machines  was  already  in  the  state  of  vague  con- 
ception. We  shall  see  what  light  has  been  thrown  upon  it 
by  the  new  theory. 

*  Some  experiments  made  by  Regnault  on  the  rapidity  of  sound,  and 
on  the  expansion  of  gases,  give  as  the  true  value  of  the  equivalent  the 
number  439, 


16 


ANIMAL  MECHANISM. 


We  have  said  that  forces  are  produced  within  the  organism. 
All  living  beings  give  out  heat  and  produce  work.  The 
disengagement  of  these  forces  is  caused  by  the  chemical 
transformation  of  food. 

In  the  living  being  it  is  possible  to  measure  approximately 
the  quantities  of  heat  and  work  produced,  and  even  to  estimate 
the  quantity  of  force  contained  in  food ;  in  order  to  do  this 
it  is  sufficient  to  apply  the  methods  which  physicists  have 
employed  in  the  estimation  of  inorganic  forces. 

Thus,  a  man  placed  for  some  time  in  a  bath  will  yield  to 
the  water  a  certain  number  of  units  of  heat,  which  may  be 
easily  measured.  Applied  to  the  moving  of  a  machine,  the 
force  of  a  man  or  an  animal  will  produce  a  number  of  kilo- 
grammetres  no  less  easily  to  be  measured.  If  the  aliment  be 
subjected  to  the  experiments  which  determine  the  heating 
power  of  different  combustibles,  it  will  be  found  that  each  of 
them  contains  a  certain  quantity  of  potential  force.  Favre  and 
Silbermann  have  supplied  most  valuable  information,  attained 
by  great  labour,  on  this  point ;  and  Frankland  has  continued 
their  investigations.  "We  now  know  the  calorific  power  of 
almost  all  the  alimentary  substances,  it  is,  therefore,  possible 
to  calculate  what  free  force  their  complete  oxidation  will  yield 
either  under  the  form  of  heat  or  under  the  form  of  work. 

But,  as  we  have  seen  with  respect  to  combustibles  employed 
for  industrial  purposes,  the  oxidation  is  not  always  complete. 
Coal  partially  consumed,  gives  solid  or  gaseous  residues, 
such  as  coke  and  oxide  of  carbon,  which,  being  oxidized  in 
a  more  complete  manner,  furnish  a  certain  quantity  of  heat. 
In  the  same  way,  the  residues  of  digestion  still  contain  non- 
disengaged  force.  All  these  forces  ought  to  be  estimated  if 
we  want  to  know  how  much  of  their  force  in  tension  has  been 
lost  by  the  alimentary  matters  in  passing  through  the  organism, 
and  how  much  ought  consequently  to  be  found  again  under 
the  form  of  force  in  action.  The  urinary  secretion  also  elimi- 
nates incompletely  transformed  products ;  the  urea  and  the 
uric  acid  contain  force  in  tension,  which  ought  to  be  taken 
into  account  in  calculations. 

The  watery  vapour  which  saturates  the  air  as  it  comes  out 
of  the  lungs  removes  from  the  organism  and  carries  away  with 


TRANSFORMATION  OF  PHYSICAL  FORCES.  17 


it  a  certain  quantity  of  heat ;  the  same  thing  takes  place  in  the 
boiler  of  a  steam-engine,  as  well  as  in  cutaneous  evaporation. 

This  complication  in  the  measure  of  force  among  organized 
beings  shows  what  difficulties  await  those  who  are  en- 
deavouring to  verify  the  principles  of  thermo- dynamics  in 
animals ;  yet,  nevertheless,  it  would  be  illogical  to  admit  with- 
out proof  that,  in  living  beings,  the  physical  forces  do  not 
obey  natural  laws.  Several  savants,  firmly  convinced  of  the 
generality  of  the  laws  of  thermo  dynamics,  have  attempted  to 
demonstrate  them  upon  the  animal  organism. 

J.  Beclard  was  the  first  who  endeavoured  to  prove  that  in 
the  muscles  of  man  heat  maybe  substituted  for  mechanical 
work,  and  vice  versa.  For  this  purpose  he  examined  the 
therm ometrical  temperature  of  two  muscles,  both  of  which 
contracted,  but  one  worked,  that  is  to  say,  raised  weights,  while 
the  other  did  not  work.  It  might  have  been  expected  that  less 
heat  would  have  been  found  in  the  first  muscle,  because  a 
portion  of  the  heat  produced  during  its  contraction  ought  to 
have  been  transformed  into  work. 

The  idea  which  governed  Beclard's  experiments  was 
assuredly  correct,  but  the  means  at  his  disposal  for  ascer- 
taining the  heating  of  the  muscles  were  altogether  insufficient. 
A  thermometer  was  applied  to  the  skin  at  the  level  of 
the  muscle,  in  order  to  give  the  measure  of  the  heat  pro- 
duced ;  thus  the  variations  of  temperature  obtained  by  Beclard 
according  as  the  muscle  worked  or  not,  were  so  slight  that  no 
real  value  could  be  attached  to  them. 

Herdenheim  obtained  clearer  results  by  operating  upon 
frogs'  muscles,  which  he  made  to  contract  with  or  without  the 
production  of  work,  ascertaining  their  temperature  by  means 
of  thermo-electric  apparatus. 

Hirn  was  bolder  in  his  experiments,  for  he  sought  to  deter- 
mine the  equivalent  of  mechanical  work  in  animated  motors. 

In  order  to  make  Hirn's  experiment  comprehensible,  let  us 
consider  the  simpler  case  of  a  mechanician  desiring  to  establish 
the  thermal  equivalent  of  the  work  of  a  steam  engine,  knowing 
how  much  fuel  it  has  burned,  what  heat  has  beeu  given  out, 
and  what  quantity  of  work  has  been  produced. 

First,  he  will  estimate  the  heat  whicli  should  correspond 


18 


ANIMAL  MECHANISM. 


with  the  combustion  of  the  coal  which  he  has  burned ;  he  will 
prove  that  the  heat  which  he  has  obtained  is  less  than  this, 
which  is  made  evident  by  the  disappearance  of  a  certain 
number  of  units ;  this  disappearance  he  will  attribute  to  the 
transformation  of  heat  into  work.  Now  as  he  knows  the 
number  of  kilogrammetres  produced  by  the  machine,  he  will 
only  have  to  divide  this  number  by  that  of  the  units  of  heat 
which  have  disappeared,  in  order  to  find  the  number  of 
kilogrammetres  equivalent  to  each  of  them. 

Hirn  believed  that  the  combustion  effected,  the  heat  given 
out,  and  the  mechanical  work  produced  by  a  man  could  be 
estimated  at  the  same  time.  He  enclosed  the  subject  in  a 
hermetically  closed  chamber,  and  made  him  turn  a  wheel 
which  could,  at  choice,  revolve  with  or  without  doing  work. 

The  air  of  the  chamber  being  analysed,  showed  what 
quantity  of  carbonic  acid  had  been  given  out ;  from  thence 
were  deduced  the  combustion  produced  and  the  number  of 
units  of  heat  to  which  that  combustion  ought  to  have  corre- 
sponded. 

The  heat  given  out  in  the  chamber  was  ascertained  by  the 
ordinary  calorimetric  processes  ;  it  was,  in  proportion  to  the 
work  produced,  sensibly  inferior  to  that  which  ought  to 
have  been  found  according  to  the  quantity  of  carbonic  acid 
exhaled. 

This  disappearance  of  a  certain  number  of  units  of  heat 
was  explained  by  their  transformation  into  mechanical  work. 

From  these  experiments  Hirn  deduced  a  valuation  of  the 
mechanical  equivalent  of  heat  for  animated  motors ;  but  the 
number  which  he  obtained  differed  considerably  from  that 
which  has  been  established  by  physicists.  This  difference  is  in 
no  wise  surprising  when  we  think  of  all  the  causes  of  error 
which  are  united  in  such  an  experiment.  There  may  have  been 
an  error  concerning  the  quantity  of  carbonic  acid  exhaled ;  an 
error  concerning  the  nature  of  the  chemical  actions  which 
disengaged  this  carbonic  acid,  and  therefore  respecting  the 
quantity  of  heat  which  ought  to  have  accompanied  the  disen- 
gagement; an  error  in  the  estimation  of  the  heat  diffused 
through  the  calorimetric  chamber ;  finally,  an  error  as  to  the 
quantity  of  mechanical  work  produced  by  the  subject.  In 


ANIMAL  HEAT. 


19 


fact,  while  it  is  relatively  easy  to  estimate  the  work  of  our 
muscles  when  employed  in  lifting  a  burden,  there  are  other 
muscular  actions  which  constitute  an  important  sum  of  work 
and  which  we  do  not  yet  know  how  to  value  with  precision  ; 
we  allude  to  the  movements  of  the  circulation,  and  especially 
to  those  produced  by  the  breathing  apparatus. 

The  remarks  which  we  have  made  upon  the  greater  number 
of  the  physiological  experiments  from  which  it  has  been  sought 
to  establish  numerical  data,  apply  to  that  of  Him.  But 
though  it  cannot  furnish  an  exact  determination,  this  ex- 
periment at  least  enables  us  to  perceive  the  manner  in  which 
the  phenomena  vary;  it  shows  that  a  certain  quantity  of  heat 
always  disappears  from  the  organism  when  external  work 
is  produced.  No  greater  precision  could  be  obtained  in  the 
measure  of  thermo  dynamic  transformation  in  the  greater 
number  of  steam-engines,  and  yet  nobody  disputes  that  in 
these  motors  heat  and  work  are  substituted  for  one  another  in 
equivalent  relations. 


CHAPTER  in. 

ON  ANIMAL  HEAT. 

Origin  of  animal  heat— Lavoisier's  theory — The  perfecting  of  this  theory 
—  Estimates  of  the  forces  contained  in  aliments,  and  in  the  secreted 
products — Difficulty  of  these  estimates — The  force  yielded  by  ali- 
mentary substances  is  transformed  partly  into  heat  and  partly  into 
work— Seat  of  combustion  in  the  organism  — Heating  of  the  glands 
and  muscles  during  their  functions  -Seat  of  calorification  —  Interven- 
tion of  the  causes  of  cooling — Animal  temperature— Automatic  regu- 
lator of  animal  temperature. 

During  a  long  period,  animal  heat  was  considered  to  be  of 
a  peculiar  kind,  distinct  from  that  which  is  manifested  in  the 
inorganic  kingdom ;  this  arose  from  certain  conditions  under 
which  the  living  tissues  become  hot  or  cold,  without  its 
being  easy  to  discover  how  this  heat  appears,  or  how  it 
disappears.     It  was  almost  natural  to  admit  that  heat  is 


20 


ANIMAL  MECHANISM. 


connected  with  influences  of  nervous  origin,  when  it  was 
seen  that  certain  violent  emotions  produce  icy  coldness  in 
human  beings,  whereas  others  bring  into  the  countenance 
sudden  heat.  Now  all  these  facts  have  found  an  explanation 
in  which  there  is  nothing  to  infringe  the  ordinary  laws  of 
physics.  In  order  to  comprehend  them  thoroughly  we  must 
pass  under  our  review  the  production  of  heat  and  its  dis- 
tribution throughout  the  various  parts  of  the  organism. 

It  has  long  since  been  established  that  aliment  is  indis  - 
pensable in  the  living  being  for  the  production  of  heat,  as  well 
as  of  muscular  power.  Inanition,  at  the  same  time  that  it 
reduces  the  strength  of  the  animal,  produces  profound  cold 
in  it.  We  owe  to  the  genius  of  Lavoisier  the  comparison 
of  the  living  organism  to  a  grate  which  burns  or  incessantly 
oxidizes  substances  taken  from  without,  by  borrowing  from 
the  atmosphere  the  oxygen  requisite  for  these  transforma- 
tions. This  theory  has  triumphed  over  all  the  attacks  which 
have  been  made  upon  it,  and  their  only  result  has  been  the 
perfecting  of  its  details. 

Let  us  reduce  to  its  true  proportions  the  comparison  of  the 
living  organism  with  a  burning  grate.  In  both,  an  oxidable 
matter  finds  itself  placed  in  relation  with  oxygen  ;  but  while, 
in  a  grate,  the  natural  gas  comes  in  contact  with  the  com- 
bustible previously  raised  to  an  elevated  temperature,  in  the 
organism  the  gas  dissolved  in  the  blood  comes  in  contact  with 
materials  which  are  themselves  dissolved  in  that  liquid,  or 
which  have  deeply  entered  into  the  tissue  of  the  organs. 
Thus,  the  circulation  transports  into  every  part  of  the 
organism  the  elements  which  are  necessary  to  the  disengage- 
ment of  force.  These  bodies  remain  in  contact,  without  acting 
one  upon  the  other,  until  the  moment  arrives  when  a  specific 
action  brings  about  their  combination.  This  office,  analogous 
to  that  of  the  spark  which  kindles  the  flame,  or  to  that  of 
the  cap  which  discharges  gunpowder,  belongs  to  the  nervous 
system. 

When  the  oxidation  is  at  an  end,  and  the  forces  necessary 
to  the  functions  have  been  set  at  liberty,  there  remain  in  the 
tissues  certain  products  which  have  become  useless,  and  which 
may  be  compared  to  the  ashes  in  the  grate  and  to  the  gases 


ANIMAL  HEAT. 


21 


which  go  up  the  chimney.  These  products  must  be  elimi- 
nated. Again,  the  circulation  undertakes  this  office ;  the 
blood  dissolves  the  carbonic  acid  and  the  salts  which  are  the 
ultimate  products  of  organic  oxidation,  and  then  carries 
them,  in  its  perpetual  course,  to  the  eliminating  organs,  the 
lungs  and  the  glands. 

So  long  as  it  remained  unsuspected  that  heat  and  mechanical 
work  could  be  substituted  for  each  other,  an  attempt  was 
made  to  account  for  all  the  combustions  which  take  place 
in  the  living  organism,  by  estimating  the  quantity  of  heat 
discharged  by  an  animal  in  a  given  time.  Physicists  and 
physiologists  made  great  efforts  to  determine  this  illusory 
equality  between  the  theoretical  heat,  which  corresponded 
with  the  combustions  which  take  place  in  the  organism,  and 
the  quantity  of  heat  furnished  by  the  animal  under  experi- 
ment. 

Just  as  a  machine,  when  it  is  working,  furnishes  less  heat 
to  the  calorimeter  than-  would  be  given  out  by  a  simple  grate 
consuming  the  same  quantity  of  combustible  matter,  so  the 
living  being  gives  out  less  heat  in  proportion  as  it  executes 
more  mechanical  work.  We  have  seen,  b}r  Hirn's  experiments, 
that  it  is  solely  according  to  the  difference  which  exists 
between  the  heat  experimentally  obtained  and  that  theo- 
retically estimated,  that  we  now  endeavour  to  find  the  value 
of  the  equivalent  of  mechanical  work  in  living  beings. 

Whatever  may  be  the  varied  manifestations  of  force  in  the 
organism,  a  certain  portion  of  that  force  always  appears 
under  the  form  of  heat,  and  this  it  is  which  gives  to  animals 
a  higher  temperature  than  that  of  the  medium  in  which  they 
live. 

May  we  not,  by  ascertaining  the  temperature  of  the  different 
parts  of  the  body  of  the  animal,  discover  the  points  at  which 
heat  is  formed,  and  define  the  actual  seat  of  those  com- 
bustions of  which  we  establish  only  the  distant  results  ? 

It  is  now  demonstrated  that  the  lungs,  by  which  the  oxygen 
of  the  air  penetrates  into  the  organism,  are  not  the  seat  of 
combustion,  because  the  blood  which  comes  out  of  that  organ 
is,  in  general,  colder  than  that  which  has  gone  into  it.  If 
two  thermometers  or  thermometrical  needles  be  introduced 


£2  ANIMAL  MECHANISM. 


into  the  heart  of  an  animal,  in  order  to  ascertain  the  tempe- 
rature of  the  blood  which  is  returning  through  -all  the  veins 
of  the  body  into  the  right  cavities,  and  that  of  the  blood  which 
is  coming  into  the  left  cavities  from  the  lungs,  we  find  that 
the  blood  of  the  right-hand  side  of  the  heart  is  the  warmer  ; 
so  that  it  follows  that  heat  is  principally  produced  along  the 
course  of  the  great  circulation. 

If  we  would  more  particularly  localize  the  origin  of  heat, 
we  must  take  a  special  organ  and  investigate,  in  a  com- 
parative manner,  the  temperature  of  the  blood  which  comes 
to  it  through  the  arteries,  and  goes  out  of  it  through  the 
veins.  Thus  it  has  been  recognized  that  the  muscles,  in 
action,  and  the  glands  while  they  are  secreting,  are  organs 
for  the  production  of  heat ;  and  in  them  the  most  energetic 
chemical  action  takes  place. 

But  we  must  not  expect,  when  examining  all  the  muscles  or 
all  the  glands  at  the  moment  of  their  action,  to  find  an  un- 
varying elevation  in  the  temperature  of  their  venous  blood. 
A  third  element  enters  into  the  problem ;  it  is  the  loss  of 
heat  which  takes  place  while  the  blood  is  passing  through  the 
organ.  Now,  all  portions  of  the  body  are  not  equally  sub- 
jected to  loss  of  heat ;  the  most  superficial  are  the  most 
exposed  to  them,  while  the  deeper  organs  are  sheltered 
against  the  causes  of  cold.*  Under  these  condition^  every  dis- 
engagement of  heat  in  the  glands  ought  to  be  represented  by 
an  elevation  of  temperature  in  the  venous  blood.  If,  on  the 
contrary,  we  lay  the  sublingual  gland  bare,  in  cold  weather, 
and  investigate  the  temperature  of  the  blood  in  the  veins  of 
that  gland,  we  shall  find  the  blood  colder  than  that  which 
has  entered  through  the  arteries.  Must  we  conclude  from 
thence  that  there  has  been  no  disengagement  of  heat  in  that 
gland  ?  In  no  wise.  We  must  simply  admit  that  the  loss 
of  heat  has  exceeded  its  production. 

In  short,  heat  appears  to  be  produced  in  all  the  organs, 
but  in  various  degrees,  according  to  the  intensity  of  the 

*  "When  we  wish  to  ascertain  the  increase  of  temperature  of  the  blood 
in  the  glands,  we  must  choose,  for  this  investigation,  the  blood  of  the 
veins  of  the  liver  or  the  kidneys,  organs  sheltered  from  cooling  influences. 


ANIMAL  HEAT. 


23 


chemical  action  which  takes  place  in  them.  The  temperature 
of  an  organ  necessarily  results  from  the  heat  supplied  to  it 
by  the  blood,  from  that  which  has  been  produced  in  its 
interior,  and  from  that  which  it  has  lost.  Thus  it  is  that 
certain  veins,  those  of  the  limbs,  for  example,  bring  back 
blood  colder  than  that  of  the  corresponding  arteries ;  whilst 
others,  like  the  sub-hepatic  veins  which  leave  the  liver,  bring 
back  blood  warmer  than  that  which  has  entered  the  hepatic 
gland.  In  fact,  after  all  compensations  are  made,  the  heated 
venous  blood  predominates  in  the  living  organism  over  the 
cooled  blood;  so  that  it  re-enters  the  heart  lj°  warmer  than 
when  it  came  out  of  it. 

This  leads  us  to  study  the  question  of  the  temperature  of 
animals. 

Among  the  different  animal  species,  some,  while  producing 
heat,  are  subject  to  the  variations  of  the  surrounding  tem- 
perature, so  that  they  have  been  called  cold  blooded.  They  are 
now  called  animals  of  variable  temperature,  which  is  more 
exact.  As  for  the  animals  called  warm  blooded,  they  possess 
the  singular  property  of  having  the  blood  in  the  deeper 
portions  of  their  bodies  almost  always  at  the  same  tempera- 
ture, notwithstanding  the  variations  of  the  external  heat. 
Thus,  a  man,  sailing  from  the  polar  regions  to  the  equator, 
may  be  subject,  in  a  few  weeks,  to  changes  of  30°  in  the 
surrounding  temperature,  but  his  blood  remains  at  about 
38°. 

It  is  easy  to  understand  that  in  tho  midst  of  incessant 
variations  in  the  production  of  heat  inside  the  organism, 
and  of  the  no  less  great  variations  in  the  causes  of  its 
waste,  such  uniformity  can  only  be  obtained  by  means  of  a 
regulator  of  the  temperature.  We  shall  now  proceed  to  certain 
developments  of  the  wonderful  functions  of  the  regulator  of 
the  animal  temperature. 

Human  industry  has  often  found  it  difficult  to  provide  fixed 
temperatures,  or  at  least  to  counterbalance  the  causes  of  ex- 
cessive heat  and  cold.  A  hot-house  must  neither  fall  below, 
nor  rise  above  a  certain  temperature.  But  this  problem  is 
relatively  a  simple  one ;  the  hot- house  is  always  warmer 
than  the  external  air ;  it  can  only  be  subjected  to  more  or  less 


24 


ANIMAL  MECHANISM. 


intense  causes  of  cooling,  which,  may  be  compensated  by  a 
suitable  variation  of  heat.  Bunsen's  regulator  solves  this 
problem  satisfactorily,  by  regulating  the  supply  of  gas  which 
serves  as  a  combustible,  augmenting  it  if  the  inclosed  air 
tends  to  grow  cold,  diminishing  it  in  the  opposite  case. 

In  the  animal  economy,  two  orders  of  influences  tend  in- 
cessantly to  cause  variation  of  temperature  in  its  production 
and  in  its  expenditure.  Causes  of  loss  of  temperature  exist, 
as  in  the  instance  just  mentioned.  The  temperature  of  the 
surrounding  air,  against  which  our  clothing  protects  us  more 
or  less  efficiently,  on  the  one  hand,  and  the  more  or  less 
easy  evaporation  by  means  of  cutaneous  perspiration,  accord- 
ing to  the  hygro metrical  state  of  the  atmosphere  on  the 
other ;  the  action  of  the  wind,  or  of  air-currents ;  the  tem- 
perature of  the  baths  which  we  take,  all  these  different 
causes  tend  to  increase  or  diminish  the  waste  of  heat  to 
which  the  body  is  subject.  To  these  influences  must  be  added 
those  of  the  hot  or  cold  food  which  we  eat ;  of  the  hot  or 
cold  air  introduced  into  our  lungs  by  respiration,  &c.  All 
these  constitute  in  general  the  causes  of  loss  of  heat. 

Another  variable  element  in  the  establishment  of  the 
animal  temperature  is  the  production  of  heat  which  takes 
place  in  the  interior  of  the  organism,  and  which,  as  well  as 
its  loss,  varies  under  numerous  influences.  The  aliments  of 
which  we  partake,  act,  through  their  nature  and  quantity,  on 
this  production  of  internal  heat ;  the  activity  of  the  glands 
causes  a  discharge  of  caloric ;  and  the  case  is  the  same  with 
respect  to  muscular  action,  which  cannot  be  produced  without 
the  heating  of  the  muscle. 

It  is  true  that  within  certain  limits  our  senses  warn  us  to 
restrict  the  production  of  heat,  or  to  promote  it,  according  as 
external  influences  diminish  or  augment  its  waste.  Thus, 
the  amount  of  food  taken  varies  with  climate,  so  that  the  en- 
forced sobriety  of  the  dweller  in  hot  countries  has  no  raison 
d'etre  in  cold  ones.  Obligatory  idleness  during  the  heat 
of  the  day  under  a  burning  sky  is  one  manner  of  diminishing 
the  production  of  heat;  the  Northmen,  on  the  contrary,  en- 
deavour to  compensate,  by  muscular  activity,  for  the  cold  to 
which  they  are  subjected. 


ANIMAL  HEAT. 


25 


But  these  are  not  the  true  regulators  of  the  animal 
temperature.  Our  will  commands  all  those  actions  whose 
influence  may  be  favourable  to  the  regulation  of  our  tempe- 
rature ;  but,  in  general,  Nature,  in  order  to  secure  the  indis- 
pensable functions  of  life,  removes  them  from  the  control  of 
our  will.  It  is  in  an  automatic  apparatus  that  we  shall  find 
the  real  regulator  of  temperature. 

This  apparatus  must  obey  external  and  internal  influences 
at  the  same  time,  it  must  retain  heat  when  it  tends  to  be 
dissipated  too  rapidly,  and,  on  the  other  hand,  it  must  facili- 
tate its  decrease  when  it  is  produced  too  abundantly  within 
the  organism. 

This  double  end  is  achieved  by  a  property  of  the  circu- 
latory system  :  the  blood  vessels,  animated  by  nerves  whose 
action  has  been  revealed  by  M.  CI.  Bernard,  close  under  the 
influence  of  cold,  and  open  under  the  effect  of  heat.  This 
property  regulates  the  course  of  the  blood  in  each  of  the 
organs,  and  at  the  same  time  the  temperature  throughout  the 
entire  economy. . 

Let  us  take  an  animal  which  has  just  been  killed ;  the 
circulation  of  the  blood  is  stopped,  and  with  it  all  the 
functions.  This  animal,  if  placed  in  a  low  temperature, 
becomes  cold.  According  to  physical  laws,  the  extremities  of 
the  limbs  and  the  surface  of  the  body  will  lose  heat  in  the 
first  instance,  while  the  central  portions  will  still  remain  very 
hot,  being  sheltered  by  the  more  superficial  layers  against  the 
causes  of  loss  of  heat.  This  corpse  will  resemble  an  inert 
body  which  has  been  heated,  and  is  growing  cold.  The  cir- 
culation of  the  blood  opposes  itself,  during  life,  to  the 
unequal  partition  of  heat  over  the  various  points  of  the 
organism  ;  bringing  the  arterial  blood,  at  a  temperature 
of  nearly  38°  (centigrade),  to  the  superficial  portions,  it  warms 
them  when  the  external  temperature  tends  to  chill  them.  On 
the  other  hand,  if,  in  the  living  animal,  the  production  of 
heat  has  been  augmented,  the  circulation  opposes  the  inde- 
finite heating  of  the  central  regions  of  the  body  ;  it  brings 
that  heat  to  the  surface,  where  it  is  lost  in  contact  with  the 
external  colder  medium. 

The  effect  of  the  circulation  of  the  blood  is  therefore  to 


26 


ANIMAL  MECHANISM. 


render  the  temperature  of  the  organism  uniform.  But  this 
uniformity  is  never  complete;  in  fact,  except  in  the  case  of  the 
animal's  being  in  a  vapour  bath  at  38°,  and  losing  none  of 
its  heat,  the  surface  of  the  body  is  always  colder  than  the 
interior,  but  no  ill  effect  is  produced  by  the  chill,  which  does 
not  act  upon  the  essential  organs. 

If  the  circulation  of  the  blood  were  of  equal  swiftness  in  every 
part,  such  a  uniformity  would  not  result  in  the  preservation  of 
the  uniform  temperature  necessary  for  the  internal  regions  of 
the  body;  we  should  then  merely  see  it  exposed  to  more  general 
elevations  and  depressions  of  temperature,  according  to  the  re- 
spective predominance  of  causes  of  heat  or  the  loss  of  it.  To 
produce  uniformity  of  central  heat  it  is  indispensable  that  some 
influence  should  augment  the  rapidity  of  the  circulation 
each  time  that  the  organism  produces  more  heat,  or  that  the 
elevation  of  the  surroundiDg  temperature  diminishes  the  causes 
of  cooling.  Circulation  in  the  superficial  portions  of  the  body 
is  extremely  variable,  as  we  may  ascertain  by  observing  the 
varying  aspects  of  those  portions,  which  are  sometimes  red, 
hot,  and  swollen,  sometimes  pale,  cold,  and  shrunken,  accord- 
ing to  the  more  or  less  abundance  of  the  blood  which  circu- 
lates in  them.  This  variability  depends  upon  the  contraction 
or  the  relaxation  of  the  little  arteries,  whose  muscular  sheaths 
obey  special  nerves.  When,  under  the  influence  of  these  nerves, 
named  vaso-motors,  the  vessels  contract,  circulation  slackens, 
while  by  a  contrary  action,  the  relaxation  of  the  vessels  ac- 
celerates the  course  of  the  blood.  Now,  it  is  the  tempera- 
ture itself  which  most  generally  acts  in  regulating  this  state 
of  contraction  or  relaxation  of  the  vessels,  so  that  the  animal 
temperature  possesses  in  reality  an  automatic  regulator. 

Every  one  has  observed  the  influence  of  heat  and  cold  on 
the  circulation  in  the  skin.  If  we  dip  one  hand  in  hot,  and 
the  other  in  cold  water,  the  first  will  grow  red  and  the  second 
pale ;  heat  has,  therefore,  the  effect  of  relaxing,  and  cold  of 
contracting  the  vessels.  In  other  words,  according  to  what  we 
have  already  seen,  heat,  by  its  action  upon  the  circulation, 
favours  the  loss  of  heat ;  while  cold  acts  in  an  inverse  sense, 
and  tends  to  diminish  the  intensity  of  the  chilling  process. 
And  it  is  not  only  under  the  influence  of  the  variations  of  the 


ANIMAL  MOTION. 


27 


external  temperature  that  these  effects  are  produced ;  they  are 
equally  observed  when  the  animal  heat  varies  in  its  produc- 
tion. The  heating  of  the  organism  which  accompanies 
muscular  activity,  or  which  results  from  taking  very  hH 
drinks,  produces  the  acceleration  in  the  superficial  circulation, 
which  throws  out  this  excess  of  heat  to  the  surface.  Inanition, 
muscular  repose,  the  drinking  of  iced  waters,  &c,  slacken  the 
circulation  near  the  surface  and  check  its  cooling  action. 

Such  are,  as  far  as  we  can  explain  them  in  a  short  chapter, 
the  origin  and  the  distribution  of  heat  in  the  animal  organism. 
The  part  played  by  the  circulation  of  the  blood  in  the  distri- 
bution of  heat,  perhaps  demands  more  ample  details ;  and, 
indeed,  we  have  treated  it  more  fully  elsewhere.*  In  the 
present  chapter  we  have  studied  heat  only  as  manifestation  of 
force,  and  have  merely  designed  to  show  that,  notwithstanding 
all  appearances,  heat  is  of  the  same  nature  in  the  inorganic 
world  and  in  organised  beings. 


CHAPTER  IV. 

ANIMAL  MOTION. 

Motion  is  the  most  apparent  characteristic  of  life  ;  it  acts  on  solids, 
liquids,  and  gases — Distinction  between  the  motions  of  organic  and 
animal  life — We  shall  treat  of  animal  motion  only— Structure  of  the 
muscles — Undulating  appearance  of  the  still  living  fibre —Muscular 
wave— Concussion  and  myography — Multiplicity  of  acts  of  contrac- 
tion— Intensity  of  contraction  in  its  relations  to  the  frequency  of 
muscular  shocks — Characteristics  of  fibre  at  different  points  of  the 
body. 

Motion  is  the  most  apparent  of  the  characteristics  of  life ; 
it  manifests  itself  in  all  the  functions ;  it  is  even  the  essence  of 
several  of  them.   It  would  occupy  much  space  to  explain  the 

*  Physiologie  mid-kale  de  la  Circulation  du  Sang.  Taris,  1803  ;  and 
Theorie  physiologique  du  CJwlera,  Gazette  Hebdomadaire  de  Medeeine. 
1867. 


28 


ANIMAL  MECHANISM. 


mechanism  by  which  the  blood  circulates  in  the  vessels,  how 
air  penetrates  into  the  lungs,  and  escapes  from  them  alter- 
nately, how  the  intestines  and  the  glands  are  perpetually 
affected  by  slow  and  prolonged  contractions.  All  these  move- 
ments take  place  within  the  organs  without  the  exercise  of  the 
will ;  frequently  even  the  individual  in  whom  they  occur  is 
unconscious  of  them ;  these  are  the  acts  of  organic  life. 

Other  movements  are  subjected  to  our  will,  which  regulates 
their  speed,  energy,  and  duration;  these  are  the  muscular 
actions  of  locomotion,  and  the  different  acts  of  the  life  of  rela- 
tion. We  shall  treat  specially  of  this  order  of  phenomena, 
which  are  more  easy  to  observe,  and  to  analyse.  Suffice  it 
here  to  say  that  the  absolute  division  between  the  acts  of 
organic  life  and  those  of  the  life  of  relation  ought  not  to  be 
accepted  unreservedly.  Bichat,  who  established  it,  based  it 
upon  anatomical  and  functional  differences  which  are  of  less 
importance  now  than  they  were  in  his  time.  The  mus- 
cular element  of  organic  life  is  unstriped  fibre  obedient  to  the 
nerves  of  a  particular  system  called  the  great  sympathetic, 
on  which  the  will  has  no  action  ;  motions  produced  by  this 
kind  of  fibre  are  manifested  some  time  after  the  excitement  of 
the  nerve  or  of  the  muscle,  and  continue  for  a  considerable 
time.  In  fact,  the  object  of  those  acts  which  are  intended  to 
maintain  the  life  of  the  individual  imprints  upon  them  a 
special  character.  The  muscular  element  of  the  life  of  rela- 
tion consists  of  a  fibre  of  striated  appearance,  whose  action, 
under  the  control  of  the  will,  is  dependent  upon  nerves 
emanating  directly  from  the  brain  or  from  the  spinal  marrow. 
These  movements  become  evident  rapidly  as  soon  as  they  are 
provoked  by  excitement ;  they  are  of  brief  duration,  and  are, 
generally,  not  indispensable  to  the  maintenance  of  the  life  of 
the  animal. 

Although  this  distinction  is,  in  a  general  way  exact,  it  is 
plain  that  it  is  too  arbitrary,  and  that  numerous  exceptions 
to  the  anatomical  and  physiological  laws  which  it  tends  to 
establish  may  be  quoted.  Thus,  the  heart,  an  organ  directly 
indispensable  to  organic  life,  and  not  under  the  governance  of 
the  will,  is  a  structure  which  much  resembles  the  voluntary 
muscles.  Certain  fishes  of  the  genus  tinea  have  striated  muscles 


ANIMAL  MOTION. 


29 


in  the  large  intestine,  as  Ed.  Weber  has  pointed  out.  Very 
often,  on  the  other  hand,  the  will  has  no  power  over  certain 
muscles  which,  by  their  structure,  and  by  the  nature  of  the 
nerves  which  animate  them,  belong  to  the  system  of  the  life 
of  relation.  Habit,  besides,  by  repeated  exercise,  appears  to 
extend  the  action  of  the  will  over  the  muscles,  almost 
indefinitely.  The  young  animal  shows,  by  the  awkwardness 
of  his  movements,  that  he  is  not  in  full  possession  of  his 
muscular  functions ;  he  seems  to  have  to  study  the  simplest 
acts,  and  performs  them  badly ;  while  the  gymnast,  or  the 
skilled  piano  forte-player  executes  prodigies  of  agility,  strength, 
or  precision,  without  any  apparent  effort  of  the  will  propor- 
tionate to  the  result  obtained.  Many  physiologists  think,  and 
we  are  of  the  same  opinion,  that  there  exist  in  the  brain, 
and  in  the  spinal  marrow,  centres  of  nervous  action  which 
acquire  certain  powers,  by  force  of  habit.  They  attain  to  the 
command  and  co-ordination  of  certain  groups  of  movements 
without  the  complete  participation  of  that  portion  of  the  brain 
which  presides  over  reasoning  and  the  consciousness  of  our 
actions. 

Let  us  lay  aside  these  questions,  which  are  still  under  inves- 
tigation, and  examine  into  the  production  of  motion  in  a 
voluntary  muscle.  The  organ  which  generates  motion  is 
composed  of  several  elements.  Simple  as  it  is  supposed  to 
be,  it  requires  the  intervention  of  muscular  fibre,  of  the  blood 
vessels,  which  unceasingly  convey  to  it  the  chemical  elements 
at  whose  expense  the  motion  is  to  be  produced,  and  finally,  of 
the  nerve  which  excites  motion  in  the  fibre. 

When  the  physiologist  desires  to  analyse  the  actions 
which  take  place  in  the  muscles,  he  does  not  deal,  in  the  first 
place,  with  voluntary  motions,  whose  complexity  is  too  great. 
The  operator  isolates  a  muscle,  and  induces  motion  in  it.  by 
bringing  to  act  upon  its  nerve  artificial  excitements  which  he 
has  under  his  control. 

To  give  an  idea  of  the  part  played  by  each  of  the  elements 
of  the  motive  apparatus  in  the  production  of  movement,  it  is 
sufficient  to  operate  upon  the  leg  of  a  frog.  13y  laying  bare 
and  severing  the  sciatic  nerve,  the  influence  of  will  upon  the 
muscle  may  be  suppressed,  so  that  the  latter  will  only  execute 


30 


ANIMAL  MECHANISM. 


such  motions  as  are  produced  by  excitation,  electric  or 
otherwise,  applied  to  the  portion  of  the  nerve  which  remains 
in  communication  with  it.  On  the  sides  of  the  sciatic  nerve 
are  an  artery  and  a  vein.  Compression  of  the  artery  will 
prevent  the  blood  from  reaching  the  muscle ;  compression  of 
the  vein  will  produce  stagnation  of  the  blood.  The  influences 
which  different  states  of  circulation  produce  upon  the  muscular 
function  may  then  be  observed ;  and,  finally,  by  making  an 
incision  in  the  skin  of  the  foot,  the  muscle  will  be  laid  bare, 
and  cold,  heat,  or  the  various  poisonous  substances  by  which 
its  action  is  modified,  may  be  brought  to  bear  directly  upon  it. 

When  the  nerve  of  a  frog  thus  prepared  is  excited  by  an 
electric  discharge,  a  very  brief  convulsive  movement  in  the 
muscle  is  produced;  this  motion  is  called  Zuckung  by  the 
German  physiologists,  and  we  propose  to  call  it  shock,  in 
order  to  distinguish  it  from  true  contraction.  It  is  so  rapid 
that  its  phases  cannot  be  distinguished  by  the  eye,  so  that,  to 
appreciate  its  characteristics  aright,  recourse  must  be  had  to 
special  instruments.  Registering  apparatus  only  can  supply 
this  need,  for  they  faithfully  render  all  the  phases  of  motion 
communicated  to  them.  The  general  disposition  of  these  forms 
of  apparatus,  which  for  a  long  time  were  used  almost  exclusively 
in  the  service  of  meteorology,  is  generally  known.  The 
indications  of  the  barometer,  of  the  thermometer,  of  the  force 
or  the  direction  of  the  wind,  of  the  quantity  of  rainfall,  &c. , 
register  themselves  under  the  form  of  a  curve  which,  accord- 
ing as  it  is  elevated  or  depressed,  expresses  the  increase  or 
diminution  of  intensity  of  the  phenomenon  to  be  registered. 
The  time  during  which  these  variations  are  accomplished  may 
be  estimated  by  the  length  occupied  by  the  curve  upon  the 
paper,  which  travels  in  front  of  the  marking  pen  with  an 
ascertained  and  perfectly  regular  speed. 

The  use  of  instruments  of  the  same  kind  has  been  introduced 
into  physiology  by  Volkmann,  Ludwig,  and  Helmholtz.  We 
have  endeavoured  to  extend  the  employment  of  them  to  a  great 
number  of  phenomena,  and  we  have  constructed  many  instru- 
ments whose  description  would  be  out  of  place  here.  The 
apparatus  which  registers  muscular  motions  bears  the  name 
of  myograph ;  it  shows  the  disturbance  of  the  muscle  by 


ANIMAL  MOTION. 


81 


means  of  a  curve  w  Inch  readily  allows  us  to  study  its  phases. 
M'e  have  fully  explained  elsewhere  the  nature  of  this  in- 
strument, the  experiments  for  which  it  is  suitable,  and 
the  results  which  it  gives.*  At  present  we  shall  limit  our- 
selves to  a  summary  description  of  the  chief  results  of 
myography. 


Fio.  2.— Tho  Myograph. 


In  order  to  explain  thoroughly  the  function  of  the  appa- 
ratus, let  us  reduce  it  in  the  first  place  to  its  essential 
elements.  Fig.  2  shows  a  muscle  of  the  calf  of  a  frog's  leg,  m, 
suspended  by  a  clip  by  means  of  the  bone  to  which  the  upper 
part  of  the  muscle  is  attached.  The  tendon,  t,  of  the  muscle 
has  been  cut  and  then  tied  by  a  thread  to  the  lever,  L,  one  end 
of  which  can  be  raised  or  lowered  while  the  other  is  fixed  ;  tin1 
nerve,  n,  is  susceptible  of  electric  excitement,  which  produces 
certain  contractions  followed  by  relaxations  in  the  muscle,  that 
is  to  say  shocks.  Each  of  these  movements  of  the  muscle  is 
communicated  to  the  lever,  which  is  raised  or  lowered,  ampli- 


*  Du  Mouvcment  dans  Its  Functions  de  la  Vic.    Paris,  1867  :  G.  Bailliere. 


32 


ANIMAL  MECHANISM. 


fying  at  its  extremity  the  motions  which  it  has  received. 
This  lever,  which  ends  in  a  point,  traces  on  a  turning  cylinder 
certain  curves,  which,  when  they  are  raised,  indicate  the  con- 
traction of  the  muscle,  and  when  they  are  lowered,  show 
its  return  to  its  primitive  length. 

With  the  arrangement  which  we  have  made  in  the  myograph 
a  muscle  may  be  operated  upon  without  being  detached  from 
the  animal,  which  allows  of  the  organ  being  left  in  the  normal 
conditions  of  its  function. 

In  Fig.  3  the  frog  is  represented  in  the  experiment,  fixed, 
by  means  of  pins,  on  a  piece  of  cork. 


Fig.  3. — Marey's  Myograph. 


The  brain  and  spinal  marrow  have  been  previously  destroyed, 
so  as  to  extinguish  all  voluntary  movement  and  sensibility. 
Although,  to  all  appearance,  the  animal  is  dead,  it  will  never- 


OF  MOVEMENT  IN  ANIMALS. 


theless  retain  for  several  hours  the  circulation  of  the  blood, 
and  the  power  of  motion  under  the  influence  of  electric 
discharges.  An  electric  excitator  conveys  the  current  from  an 
induction  coil  to  the  nerve  of  the  frog. 

In  order  to  register  these  movements  and  to  depict  them 
by  curves  which  express  their  different  phases,  they  are  trans- 
mitted to  the  myograph  in  the  manner  already  described. 
The  tendon  of  the  muscle  is  cut,  and  connected  by  a  wire 
which  is  fastened  at  the  other  end  to  the  lever  of  the 
registering  apparatus ;  the  latter  moves  in  a  horizontal  plane, 
when  the  contractile  force  of  the  muscle  is  exerted  upon  it. 
As  soon  as  the  muscle  ceases  to  act,  the  lever  returns,  under 
the  pressure  of  a  spring,  to  its  original  position.  At  the  free 
extremity  of  the  lever  is  a  point  which  traces,  on  a  turning 
cylinder  covered  with  smoked  paper,  the  motions  produced  by 
the  alternate  contraction  and  relaxation  of  the  muscle. 

When  the  cylinder  is  motionless,  the  lever  traces,  for  each 
muscular  shock,  a  straight  line  which  expresses  (by  amplifying 
it  in  a  known  proportion)  the  extent  of  the  contraction  of  the 
muscle.  Several  authors  limit  themselves  to  this  kind  of 
myography,  by  which  they  ascertain  the  variations  produced  by 
different  influences  in  the  intensity  of  muscular  action.  By 
giving  the  cylinder  a  rapid  rotatory  motion,  a  curve  is  obtained 
which  expresses  by  its  height  tiie  exient  of  the  contraction, 
and  indicates  by  its  inclination,  which  constantly  varies,  the 
speed  with  which  the  muscle  passes  through  the  different 
phases  of  the  shock.  Finally,  in  order  to  obtain,  without 
confounding  them,  a  great  number  of  successive  tracings, 
the  foot  of  the  myograph  is  placed  upon  a  little  railroad 
which  works  parallel  to  the  axis  of  the  cylinder.  The 
writing  point  then  traces  an  indefinite  spiral  all  round  the 
cylinder,  and  on  this  spiral  a  number  of  regularly  graduated 
curves  (Fig.  5)  are  traced,  answering  to  a  series  of  electric 
excitations  produced  at  equal  intervals ;  each  of  these  curves 
corresponds  with  one  of  the  electric  shocks. 

If  the  speed  with  which  the  cylinder  turns  be  augmented 
or  diminished,  a  change  ensues  in  the  appearance  of  the 
curves,  which  necessarily  occupy  a  greater  or  less  space  on 
the  paper,  but  if  a  uniform  speed   in  the  rotation  of  the 


34 


ANIMAL  MECHANISM. 


cylinder  be  maintained,  the  curves  retain  the  same  form  so 
long  as  the  muscle  gives  the  same  movements. 

Not  only  are  shocks  produced  in  the  muscle  by  acting 
upon  its  nerve  by  electricity,  but  also  by  applying  electric 
excitement  to  the  muscle  itself.  Pinching,  percussion,  and 
cauterization  of  the  nerve  are  also  excitants  which  provoke 
shocks  of  the  muscle. 

The  character  of  these  movements  changes  under  certain  in- 
fluences. Fatigue  of  the  muscle,  the  cooling  of  that  organ,  the 
stoppage  of  circulation  in  its  interior,  modify  the  form  of  the 
shock,  diminish  its  force,  and  augment  its  duration.  Under 
these  influences  the  myographic  curve  passes  through  different 
forms,  such  as  1,  2,  3,  Fig.  4. 


Fig.  4.— Character  of  the  shock,  according  to  the  degree  of  fatigue  of  the 
muscle  :  1,  muscle  fresh  ;  2,  muscle  a  little  fatigued  ;  3,  muscle  still  more 
fatigued. 


Among  the  different  species  of  animals,  the  durations  of  the 
shock  vary  considerably  ;  in  the  bird  they  are  very  brief  (two 
to  three  hundredths  of  a  second).  In  man  4hey  are  longer  ; 
in  the  tortoise  and  hybernating  animals  longer  still.  Certain 
poisons  modify  the  characteristics  of  this  movement  in  so 
special  a  manner,  that  the  slightest  traces  of  those  poisons 
introduced  into  the  circulation  of  the  animal  may  be  disco- 
vered in  the  form  of  the  tracings. 

By  Fig.  5,  we  may  judge  of  the  successive  forms  which 
will  be  assumed  by  the  shocks  of  the  muscle  of  a  frog,  under 
the  influence  of  a  gradual  absorption  of  veratrine. 

These  experiments  still  reveal  only  one  fact :  it  is  that 
the  muscle  is  shortened  or  lengthened  by  a  movement  whose 


OF  MOVEMENT  IN  ANIMALS. 


36 


phases  vary  under  the  different  influences  which  we  have  just 
described. 

If  we  endeavour  to  pursue  the  study  of  this  phenomenon  of 
the  contraction  of  the  muscle,  we  see  that  it  is  only  a  change 
in  the  form  of  that  organ,  and  that  the  diminution  of  length 
is  accompanied  by  a  corresponding  dilatation  which  might 
be  expected  in  a  sensibly  incompressible  tissue.  But  the 
manner  in  which  this  dilatation  is  produced  is  curious. 


Fig.  5. — Successive  transformations  of  the  shock  of  a  muscle  becoming 
gradually  poisoned  by  veratrine.  Underneath  to  the  left  of  the  figure 
are  shown  the  first  effects  of  the  poison. 


It  has  been  long  since  observed  that  there  are  formed  upon 
living  muscles  at  the  points  where  they  are  excited,  lumps  or 
nodosities  which  run  along  the  whole  length  of  the  muscle, 
with  more  or  less  rapidity,  like  a  wave  on  the  surface  of  the 
water.  Aeby*  has  showh  that  this  is  a  normal  phenomenon, 
and,  under  the  name  of  muscular  wave,  he  has  described  this 
movement,  which,  from  the  excited  point,  passes  to  the  two 
extremities  of  the  muscle  at  the  rate  of  about  a  metre  in  a 
second.    By  means  of  an  apparatus,  which  we  have  called 

*  Untersuchnngcn  uhe.r  die,  Forfpflanzi/iufsgrsehirindi fkeit  dcr  Rcizungs  in 
der  querzgedreiften  Muskclfascra.    Braunschweig  :  1862. 


36 


ANIMAL  MECHANISM. 


myograpliical  clips,  the  reality  of  this  movement  of  the  wave 
may  be  verified  in  the  living  animal. 

When  the  wave  appears  in  the  muscle,  it  produces  con- 
traction. Daring  the  whole  of  its  passage  the  contraction 
continues,  and  when,  having  reached  the  end  of  the  muscular 
fibre,  the  wave  vanishes,  the  contraction  disappears  with  it. 

These  facts  resemble  those  which  the  microscope  reveals  in 
living  muscular  fibre.  Let  a  bundle  of  muscular  fibres  be 
taken  from  an  insect,  and  placed  under  the  objective  of  the 
microscope  (the  feet  of  coleoptera  are  well  suited  for  this 
purpose) ;  we  first  observe  the  beautiful  transverse  striation 
of  these  fibres,  and  then  we  perceive  on  their  surface  an  undu- 
latory  movement  often  alternating,  which  resembles  the  motion 
of  waves  on  the  surface  of  water.  On  examining  this 
phenomenon  more  closely,  we  see  that  the  transverse  strise 
of  the  fibre  are,  at  certain  points,  very  close  together,  which 
is  shown  in  the  figure  by  a  dilatation  of  the  fibre.  This 
is  the  wave  shown  by  the  microscope ;  the  longitudinal  con- 
densation of  the  muscle  at  this  point  gives  it  greater  opacity 
than  in  the  other  portions  (Fig.  6.)    This  opaque  wave  travels 


Fig.  6. — Appearance  presented  by  a  wave  in  muscular  fibre. 


through  the  length  of  the  fibre.  In  other  words,  the  points 
at  which  the  striae  approach  each  other  are  not  always  the 
same,  the  longitudinal  condensation  disappears  in  one  place 
whilst  it  is  produced  in  the  contiguous  parts. 

Since  the  contraction  of  the  muscle  is  accompanied  by  its 
transverse  dilatation,  we  may  study  the  characteristics  of 
the  motion  produced  in  a  muscle,  according  to  this  expansion. 
We  have  succeeded  in  registering  these  changes  in  the 
volume  of  the  muscle,  as  we  have  registered  the  changes 
in  its  length.  Under  these  conditions  we  might  study 
muscular  action  in  man  himself,  because  there  is  no  need 
of  mutilation. 

Let  us  suppose  a  muscle  held  between  the  flattened  ends  of 


OF  MOVEMENT  IN  ANIMALS. 


37 


a  clip  ;  at  each  of  its  dilatations  the  muscle  will  force  open 
the  clip,  and  this  movement  may  be  registered.  This  method 
enables  us  to  study  the  phenomenon  of  the  muscular  wave, 
and  the  speed  with  which  it  travels  throughout  the  whole 
length  of  the  muscle. 

Fig.  7  exhibits  a  bundle  of  muscle  held  at  two  points 
of  its  length  between  the  myographical  clips,  1  and  2. 
Those  instruments  are  so  constructed  that  when  their  ends 
are  pushed  apart  by  the  dilatation  of  the  muscle,  the  move- 


O.  7  —Disposition  of  a  bundle  of  muscle  between  two  pairs  of  myo- 
graptrcal  clips.  Clip  No.  1  holds  the  electric  excitaton  <>f  the  muscle.  A 
whvc  is  represented  at  the  moment  when  it  has  just  crossed  each  of  the 
clips. 

ment  compresses  a  sort  of  little  drum  which  sends  a  portion 
of  the  air  which  it  contained  through  an  india-rubber  tube 
into  a  similar  little  drum.  Fig.  7  shows  two  of  these  instru- 
ments fixed  upon  a  foot.  The  expansion  of  the  membrane 
lifts  a  registering  lever,  and  thus  gives  notice  of  the  dilatation 
of  the  muscle  at  the  point  where  it  is  compressed  by  clip 
No.  1.  The  movement  is  shown  upon  the  tracing  by  a  curve 
analogous  to  those  which  we  have  already  seen. 


38 


ANIMAL  MECHANISM. 


Let  us  suppose  that  the  muscle  is  electrically  excited  at 
the  level  of  the  first  clip  ;  notice  is  given  of  the  formation  of 
the  wave  at  that  part  of  the  muscle,  but  clip  No.  2  does 
not  yet  give  its  signal.  In  order  that  it  may  act,  the  wave, 
as  it  passes  along  the  muscle,  must  reach  it.  As  this  occurs, 
clip  No.  2  gives  the  signal  in  its  turn,  and  it  is  shown  by 
the  tracing,  that  this  second  movement  is  later  than  the  first 
by  a  certain  space  whose  duration  may  be  estimated  according 
to  the  speed  of  the  rotation  of  the  cylinder. 

The  influences  which  modify  the  intensity  and  the  duration 
of  the  muscular  shock  have  appeared  to  us  to  modify  the 
intensity  and  the  speed  of  the  propagation  of  the  wave.  Thus 
the  two  lower  curves  represented  in  Fig.  8  show  that  the 
transference  of  the  wave  is  retarded  by  cold. 


Fig.  8. — Two  determinations  of  the  speed  of  the  muscular  wave. 


The  experiment  has  been  made  upon  the  muscles  of  the 
thigh  of  a  rabbit.  The  clips  were  placed  as  far  as  pos- 
sible apart,  about  seven  centimetres.  Electricity  was  applied 
to  the  lower  extremity  of  the  muscle,  and  the  two  upper  curves 
of  Fig.  8  were  obtained.  The  interval  which  divides  those 
curves  marks  the  duration  of  the  transference  of  the  muscular 
wave.  After  the  muscle  had  been  chilled  with  ice  the  curves 
at  the  bottom  of  the  figure  were  obtained.  We  see  that  the 
transference  of  the  wave  is  slackened,  for  there  is  a  longer 
interval  between  these  curves  than  between  the  first. 

Production  of  mechanical  force  in  the  muscle. — We  have  seen 
that  chemical  action  is  the  source  of  muscular  force ;  through 


OF  MOVEMENT  IN  ANIMALS. 


39 


what  media  does  this  force  pass  before  it  becomes  mechanical 
work  ? 

In  steam  engines,  heat  is  the  necessary  medium  between 
the  oxidation  of  the  fuel  and  the  developed  mechanical  work. 
It  is  very  probable  that  the  same 
thing  takes  place  in  the  muscles. 
The  chemical  action  produced  by 
the  nerve  within  the  fibre  of  the 
muscle  disengages  heat  from  it  : 
this  heat  in  its  turn  is  itself 
partially  transformed  into  work. 
We  say  partially,  since  accord- 
ing to  the  second  principle  of 
thermo-dynamics,  heat  cannot  be 
entirely  transformed  into  me- 
chanical work. 

Certain  facts  seem  to  justify 
these  views  :  thus,  by  warming 
a  muscle,  we  change  the  form  of 
it,  and  may  see  it  contract  in 
length  as  it  expands  iu  breadth. 
These  effects  disappear  when  the 
muscle  is  cooled. 

Muscular  fibre  is  not  singular 
in  its  power  of  transforming  heat 
into  work.  India-rubber,  for  in- 
stance, has  an  analogous  property, 
and  this  substance  may  be  made 
to  imitate  the  muscular  phe- 
nomena to  a  certain  degree.  If 
we  take  a  strip  of  india-rubber 
(not  vulcanised),  and,  drawing  it 
between  the  fingers,  stretch  it  out 
to  ten  or  fifteen  times  its  original 
length,  we  see  that  it  becomes 
white,  and  of  a  pearly  lustre, 
will  become  sensibly  warm,  and 
return  to  its  original  condition,  so  that  if  we  let  go  either  of 
its  ends,  it  will  instantly  resume  its  former  length,  and  fall  to 


Fio.  9.—  Transformation  of  heat  into 
work  by  a  strip  of  india-rubber. 

At  the  same  time  the  strip 
it  will  tend  energetically  to 


10 


ANIMAL  MECHANISM. 


its  original  temperature.  According  to  our  view,  the  sensible 
heat  has  disappeared  and  become  mechanical  work.  If  we 
plunge  the  strip  when  extended  into  water,  so  as  to  deprive  it 
of  its  heat,  it  remains,  as  it  were,  congealed  in  its  extended 
state,  and  does  not  develop  any  mechanical  work.  But  if  we 
restore  to  the  elongated  strip  the  heat  which  it  had  lost,  it 
will  recover  its  elasticity  with  considerable  force.  Fig.  9 
represents  a  strip  of  india-rubber  thus  pulled  out  and  cooled. 
It  has  been  laden  with  a  weight  that  it  may  have  no  tendency 
to  recover  itself.  But,  if  we  take  the  strip  between  our  fingers, 
we  feel  it  swell  and  shorten  at  the  same  time  that  it  lifts  the 
weight ;  there  is  again  production  of  mechanical  work. 

If  we  thus  heat  the  strip  at  various  points  we  create  a 
series  of  lateral  expansions,  each  of  which  raises  a  certain 
quantity  of  the  weight.  Lastly,  if  we  heat  it  throughout  all 
its  extent,  the  strip  returns  to  its  original  dimensions,  with 
the  exception  of  the  slight  elongation  produced  by  the  sus- 
pended weight. 

Strong  analogies  exist  between  these  phenomena,  and 
those  which  take  place  in  muscular  tissue.  The  identity  would 
be  perfect  if  the  wave  which  heat  produces  on  the  strip  of 
india-rubber  were  transmitted  to  each  end.  This  transference 
implies,  in  the  muscular  fibre,  the  successive  propagation 
of  the  chemical  action  which  disengages  the  heat.  It  is  thus 
that  if  we  light  a  train  of  powder  at  one  point,  the  in- 
candescence spreads  throughout  its  entire  length. 

These  analogies  have  struck  us  as  being  remarkable  :  they 
seem  to  us  to  open  new  views  of  the  origin  of  muscular 
action. 


CONTRACTION  AND  WORK  OF  THE  MUSCLES.  41 


CHAPTER  V. 

CONTRACTION  AND  WORK  OF  THE  MUSCLES. 

The  function  of  the  nerve— Rapidity  of  the  nervous  agent— Measures  of  time 
in  physiology — Tetanus  and  muscular  contraction — Theory  of  con- 
traction— Work  of  the  muscles. 

The  experiments  described  in  the  preceding  chapter  show 
ns  the  muscle  under  artificial  conditions,  which  may,  perhaps, 
induce  us  to  suspect  the  results  which  they  furnish.  Can 
this  electrical  agent,  which  has  been  employed  to  excite 
motion,  be  assimilated  to  the  unknown  agent  which  the  will 
sends  through  the  nerves  to  command  the  muscles  to  act? 
And  these  artificially-produced  movements,  those  brief  shocks, 
always  similar  if  the  conditions  of  the  muscle  be  not  changed, 
in  what  do  they  resemble  the  motions  commanded  by  the 
will,  which  are  so  varied  in  their  form  and  their  duration  ? 
These  objections  deserve  at  least  a  brief  discussion. 

The  function  of  the  nerve.  When  a  nerve  is  excited  by  an 
electric  discharge,  the  electricity  employed  does  not  always 
pass  to  the  muscle  in  which  the  reaction  takes  place.  The 
shock  is  produced  equally  well  when  all  propagation  of  the 
electric  current  along  the  nerve  is  prevented,  and  it  exhibits 
itself  equally  when  excitants  of  a  quite  different  nature  are 
employed,  for  instance,  pinching  or  percussion.  Thus,  the 
excitant  employed  only  excites  in  the  nerve  the  transference 
of  the  agent  which  is  proper  to  that  organ.  Is  not  this 
nervous  agent  itself  electricity?  Notwithstanding  the  able 
labours  of  the  German  physiologists,  and  especially  of 
M.  Du  Bois  Reymond,  science  has  not  yet  decided  on  that 
subject.  We  know  that  electric  phenomena  are  produced  in 
the  nerve  when  it  has  been  excited  in  a  certain  way,  and 
that  their  propagation  throughout  the  nervous  cord  seems 
to  have  precisely  the  same  speed  as  that  of  the  transference 
of  the  nervous  energy  itself.  How  has  this  speed  been 
measured  ? 


42 


ANIMAL  MECHANISM. 


Helinlioltz  had  the  boldness  to  undertake  this  measurement, 
and,  by  determining  the  speed  of  the  nervous  agent,  he  has 
furnished  physiologists  with  a  method  which  enables  them  to 
measure  the  duration  of  other  phenomena  connected  with  the 
nervous  or  muscular  functions.  Thus  the  experiment  described 
above,  in  which  we  have  measured  the  speed  of  the  trans- 
ference of  the  wave  in  a  muscle,  is  only  an  application  of  the 
method  of  Helmholtz. 

In  order  to  make  the  conditions  of  this  experiment 
thoroughly  comprehensible,  let  us  make  use  of  a  comparison. 
Let  us  suppose  that  a  letter  is  despatched  from  Paris  to  go  to 
Marseilles,  and  that,  being  resident  in  the  latter  town,  we 
should  be  informed  of  the  precise  instant  at  which  the  postal 
train  leaves  Paris,  while  we  have  nothing  to  warn  us  of  its 
arrival  at  Marseilles  except  the  knowledge  of  the  moment  at 
which  the  letter  is  delivered  there.  How  can  we,  according  to 
these  data,  estimate  the  speed  of  the  mail  train?  It  is  clear 
that  the  instant  at  which  we  receive  the  letter  does  not  indi- 
cate that  of  the  arrival  of  the  train ;  for  between  that  arrival 
and  the  distribution,  many  preliminaries  take  place,  the  sorting 
of  letters,  delivery,  &c,  which  require  a  certain  time  not 
within  our  knowledge.  In  order  to  have  an  exact  idea  of  the 
speed  of  the  train  which  carries  the  mail,  we  must  receive 
a  signal  of  the  passage  of  that  train  through  an  intermediate 
station  between  Paris  and  Marseilles,  Dijon,  for  instance ; 
then  we  shall  see  that  the  distribution  of  letters  takes  place 
six  hours  sooner  after  the  departure  from  Dijon  than  after  the 
departure  from  Paris.  Knowing  the  distance  which  separates 
these  two  stations,  we  may  ascertain  from  the  time  employed 
in  traversing  it,  the  speed  of  the  train.  By  supposing  this 
speed  to  be  uniform,  we  shall  know  the  hour  at  which  the 
train  will  have  arrived  at  Marseilles,  which  will  give  us  know- 
ledge of  the  time  consumed  in  the  sorting  and  distribution  of 
the  letters. 

Helmholtz,  in  experimenting  upon  the  nervous  motive 
agent,  first  excited  the  nerve  at  a  point  very  distant  from  the 
muscle,  and  noted  the  time  which  elapsed  between  the  excite- 
ment which  despatched  the  message  carried  by  the  nerve,  and 
the  appearance  of  motion  in  the  muscle.   Then  acting  on  a 


CONTRACTION  AND  WORK  OF  THE  MUSCLES.  43 


point  of  the  nerve  very  near  to  the  muscle,  he  ascertained 
that  under  these  new  conditions  the  motion  followed  the  ex- 
citement more  closely.  The  difference  of  time  which  he 
observed  in  these  two  consecutive  experiments  measured  the 
duration  of  the  transference  of  the  nervous  agent  along  the 
known  length  of  the  nerve,  and  consequently  expressed  its 
speed,  which  varied  from  15  to  30  metres  per  second.  It 
is  feebler  in  the  frog  than  in  warm-blooded  animals. 


230 


Fio.  10.— Determination  of  the  speed  of  the  nervous  agent  in  man.  1.  Shock 
produced  when  the  nerve  has  heen  excited  very  close  to  the  muscle. 
2.  Shock  produced  by  the  excitement  of  the  nerve  at  a  farther  dist.n  co 
of  30  centimetres.  D,  Vib  ation  of  a  chronograph ic  tuning-fork  vibrating 
250  times  in  a  second,  serving  to  measure  the  time  which  corresponds  with 
the  iuterval  of  the  shocks. 


Now,  it  results  from  the  experiments  of  Helmholtz,  that  all 
the  time  which  elapses  between  the  excitement  and  the  motion 
is  not  occupied  by  the  transference  of  the  nervous  agent ;  but 
that  the  muscle,  when  it  has  received  the  order  carried  by  the 
nerve,  remains  an  instant  before  acting.  This  is  what  Helm- 
holtz calls  lost  time.  This  time  would  correspond,  in  the 
comparison  which  we  have  employed  above,  with  the  duration 
of  the  preparatory  labour  between  the  arrival  of  the  letters 
and  their  distribution. 

Physiologists  have  repeated  the  experiment  of  Helmholtz 
with  some  improvements.  In  fig.  10  tracings  may  be  seen 
which  we  have  ourselves  obtained  while  measuring  the  speed 
of  the  nervous  agent. 

Two  muscular  shocks  are  successively  registered  upon  the 
same  cylinder,  care  being  taken  that  the  nerve  shall  be  excited 
in  the  two  experiments,  at  different  points,  but  at  the  same 
instant  with  regard  to  the  rotation  of  the  cylinder;  for 
example,  at  the  precise  moment  at  which  the  point  of  the 


11 


ANIMAL  MECHANISM. 


myograph  passes  over  the  vertical  which  corresponds  with  the 
origin  of  the  lines  1  and  2. 

In  the  experiment  which  regulated  the  shock  of  line  1 ,  the 
nerve  was  excited  very  near  the  muscle.  In  that  which  was 
traced  by  the  shock  of  line  2,  the  nerve  was  excited  30  centi- 
metres farther  off.  As  the  cylinder  turns  with  a  uniform 
motion  we  can  estimate  the  time  corresponding  with  the 
distance  which  separates  the  two  shocks.  To  facilitate  the 
measurement  of  this  interval,  the  vertical  lines  indicate  the 
starting  points  of  these  shocks ;  in  fig.  1 0  the  interval  which 
separates  them  corresponds  with  a  hundredth  of  a  second, 
during  which  the  nervous  agent  has  passed  over  30  centi- 
metres of  nerve,  which  corresponds  with  a  speed  of  30  metres 
per  second.  In  order  to  measure  this  time  with  very  great 
exactitude,  we  use  a  method  invented  by  Duhamel.  It  con- 
sists in  making  the  cylinder  trace  the  vibrations  of  a  chrono- 
graphic  tuning-fork  provided  for  this  purpose  with  a  very 
hue  style,  which  scratches  on  the  sensitive  paper.  We  have 
recourse  to  this  method  in  all  our  experiments. 

Let  us  return  to  fig.  10.  If  the  interval  which  divides  the 
starting  points  of  the  two  shocks  corresponds  with  the  time 
which  the  nervous  agent  has  taken  to  pass  along  30  centi- 
metres of  nerves,  there  is  a  much  more  considerable  time, 
which,  for  each  of  the  lines  1  and  2,  is  measured  between  the 
signal  of  the  excitement  marked  by  the  first  of  the  three 
vertical  lines  and  the  first  shock.  This  is  the  lost  time  of 
Helmholtz ;  it  represents  more  than  a  hundredth  of  a  second 
in  this  experiment. 

The  greater  number  of  authors  think  that  the  speed  of  the 
nervous  agent  varies  under  certain  influences;  that  heat 
augments  it,  while  cold  and  fatigue  diminish  it. 

It  seems  to  us,  on  the  contrary,  that  this  variability  of 
duration  belongs  almost  exclusively  to  those  still  unknown 
phenomena  which  are  produced  in  the  muscle  during  the 
lost  time  of  Helmholtz. 

Just  as  the  employes  of  the  post,  fatigued  or  chilled  by  cold, 
cause  delay  in  the  distribution  of  despatches,  without  there 
having  been  any  change  in  the  speed  of  the  train  which  has 
brought  them,  so  the  muscle,  according  to  whether  it  is  rested 


CONTRACTION  AND  WORK  OF  THE  MUSCLES.  45 


or  fatigued,  heated  or  chilled,  executes  more  or  less  rapidly 
the  movement  dictated  by  the  nerve. 

Besides  this,  all  the  influences  which  cause  variation  in  the 
moment  at  which  the  shock  of  the  muscle  appears,  cause 
variation  of  speed  in  the  propagation  of  the  wave  in  its 
interior;  which  proves  that  the  conditions  which  accelerate 
or  retard  chemical  actions,  the  first  causes  of  all  these  phe- 
nomena, are  solely  concerned. 

Of  the  contraction  oj  the  muscle.  Hitherto,  we  have  applied 
to  the  nerve  only  one  single  excitation,  to  which  one  single 
motion  responded,  the  muscular  shock.  Notwithstanding  its 
brevity,  this  shock  has  an  appreciable  duration ;  in  man  it  takes 
8  or  10  hundredths  of  a  second  for  the  muscle  to  accomplish 
its  contraction ;  then  a  longer  time  for  it  to  resume  its  normal 
length  ;  after  which,  if  it  receives  a  new  order  from  a  nerve, 
it  gives  a  fresh  shock.  But  if  the  excitations  of  the  nerve 
succeed  each  other  at  such  short  intervals  that  the  muscle  has 
not  time  to  accomplish  the  first  shock  before  it  receives  a 
second,  a  special  phenomenon  is  produced ;  these  movements 
are  confounded  and  absorbed  into  a  state  of  permanent  con- 
traction, which  lasts  as  long  as  the  excitations  go  on  suc- 
ceeding each  other  at  short  intervals. 

Thus  the  shock  is  only  the  elementary  act  in  the  function  of 
the  muscle ;  it  plays  therein,  after  a  fashion,  the  same  part  as 
a  sonorous  vibration  plays  in  the  complex  phenomenon  which 
constitutes  sound.  When  the  will  ordains  a  muscular  con- 
traction, the  nerve  excites  in  the  muscle  a  series  of  shocks 
which  follow  one  another  so  closely  that  the  first  has  not  time 
to  end  before  a  second  begins,  so  that  these  elementary 
movements  combine  together  and  coalesce  to  produce  the 
contraction. 

Volta  pointed  out,  in  a  letter  to  Aldini,  this  singular  fact, 
that  a  frog  which  receives  a  series  of  excitations,  by  the  reite- 
rated contacts  of  two  heterogeneous  metals  applied  to  his 
nerve,  does  not  react  at  each  of  these  contacts,  but  undergoes 
a  sort  of  permanent  contraction.  Ed.  Weber  shows  that  the 
action  of  successive  induced  currents  is  of  the  same  kind, 
and  he  has  given  the  name  of  tetanus  to  the  state  of  the 
muscle  thus  excited.    Ilelmholtz  perceived  that  the  muscle 


46 


ANIMAL  MECHANISM. 


vibrates  in  the  depths  of  its  tissue  under  these  conditions  of 
contraction,  because  the  ear  applied  to  this  muscle  hears  a 
sound  whose  acuteness  is  exactly  determined  by  the  number 
of  the  electric  excitations  sent  to  the  muscle  in  a  second. 

By  means  of  a  very  sensitive  myograph,  we  have  been  able 
to  render  visible  the  vibrations  of  the  muscles  under  the  in- 
fluence of  tetanus-producing  shocks. 

Fig.  11  shows  how  this  fusion  of  shocks  is  manifested 
by  a  contraction  of  the  muscle,  permanent  in  appearance,  but 
in  which  the  tracing  reveals  vestiges  of  vibrations.  Vibrations 
may  be  found  in  the  tetanus  which  strychnine  produces  in  the 
muscles  of  an  animal,  as  well  as  in  that  which  is  caused  by 
the  irritation  of  a  nerve  by  heat  and  chemical  agents. 


Fig.  11.  — Gradual  coalescence  of  the  shocks  produced  by  electric  excitations  of 
increasing  frequency. 

In  short,  these  voluntary  contractions  seem  to  be  only  a 
series  of  shocks,  combining  together  by  the  rapidity  of  their 
succession. 

It  has  long  been  known  that  by  applying  the  ear  to  a 
muscle  in  a  state  of  voluntary  contraction,  we  can  hear  a 
grave  sound,  whose  tone  several  authors  have  sought  to 
determine.  Wollaston,  Houghton,  and  Dr.  Collongue  are 
almost  agreed  upon  this  tone,  which  would  correspond  to  a 
frequency  of  32  or  35  vibrations  per  second.  Helmholtz 
thinks  that  this  tone  of  32  vibrations  per  second  is  the  normal 
sound  given  out  by  the  muscle  in  contraction,  and  according 
to  his  experiments  in  electric  tetanization,  he  regards  this 


CONTRACTION  AND  WORK  OF  THE  MUSCLES.  47 


number  as  the  minimum  necessary  to  produce  the  state  of 
apparent  immobility  of  the  electrically  tetanized  muscle. 

If  voluntary  contraction,  studied  with  the  aid  of  the  myo- 
graph, furnishes  no  trace  of  vibrations,  we  must  not  be  sur- 
prised, since  the  essential  character  of  that  act  consists  in  the 
coalescence  of  shocks.  But  the  existence  of  the  sound  which 
accompanies  the  contraction  of  the  muscle  sufficiently  proves 
the  complexity  of  this  phenomenon.  Let  us  add  another  proof 
in  favour  of  this  theory.  When  a  muscle  receives  excitations 
of  equal  intensity,  the  contraction  which  results  from  them  is 
all  the  stronger  in  proportion  to  their  frequency.  Now,  in 
contracting  the  muscles  of  the  jaws  with  more  or  less  force, 
we  have  been  able  to  convince  ourselves  that  the  acuteness  of 
the  muscular  sound  increased  with  the  energy  of  the  effort. 
We  may  thus  obtain  variations  of  a  Jifth  in  the  tone  of  the 
muscular  sound. 

We  shall  also  see  hereafter  how  the  electric  state  of  the 
muscles  in  contraction  proves  still  more  the  complexity  of  this 
phenomenon. 

The  conclusion  at  which  we  have  arrived  is,  that  during 
voluntary  contraction,  the  motor  nerves  are  the  seat  of  suc- 
cessive acts,  eiich  of  which  produces  an  excitation  of  the 
muscle.  The  latter,  in  its  turn,  causes  a  series  of  acts,  each 
of  which  gives  birth  to  a  muscular  wave  producing  a  shock. 
It  is  in  the  elasticity  of  the  muscle  that  we  must  seek  for  the 
cause  of  the  coalescence  of  these  multiplied  shocks ;  they  are 
extinguished  just  as  the  jerks  of  the  piston  of  a  fire  engine 
disappear  in  the  elasticity  of  its  reservoir  of  air. 

Of  work  done  by  the  muscles.  After  having  seen  how 
mechanical  force  is  produced,  let  us  try  to  measure  it — that 
is  to  say,  to  compare  it  with  the  kilogrammetre,  the  unit  of 
measure  of  work.  If  we  suspend  a  weight  to  the  tendon 
of  a  muscle  which  we  cause  to  contract,  we  easily  obtain  the 
measure  of  work  by  multiplying  this  weight  by  the  height  to 
which  the  muscle  raises  it. 

In  animated  motors,  the  measure  of  work  is  less  easy  to 
obtain.  Sometimes,  indeed,  the  strength  of  an  animal  is 
utilized  in  the  lifting  of  a  weight,  but  the  greater  part  of  the 
acts  in  which  the  strength  of  animals  is  employed  can  only 


ANIMAL  MECHANISM. 


l>e  estimated  by  enlarging  the  definition  of  mechanical  work. 
Thus,  a  horse  which  tows  a  boat,  a  man  who  planes  a  board, 
a  bird  which  strikes  the  air  with  its  wing,  does  mechanical 
work,  and  yet  they  do  not  lift  weights.  In  order  to  reduce 
cases  of  this  kind  to  a  general  definition,  we  must  admit  as 
the  expression  of  work,  the  effort  multiplied  by  the  space  traversed. 
This  effort,  besides,  may  always  be  compared  with  the  weight, 
the  lifting  of  which  would  necessitate  an  equal  effort,  so  that 
we  say  of  a  traction  or  an  impulse,  that  it  corresponds  with 
10  or  20  kilogrammes.  When  a  workman  planes  or  turns  a 
piece  of  metal,  if  the  tool  which' he  drives  into  it  penetrates 
only  on  condition  of  receiving  an  impulse  of  one  kilogramme, 
the  workman,  in  order  to  have  effected  a  kilogrammetre  of 
work,  ought  to  have  detached  from  the  mass  a  shaving  of  a 
metre  in  length.  A  horse  which  tows  a  boat  with  20  kilo- 
gramme force,  will  have  employed  a  force  of  20,000  kilo- 
grammetres  when  he  has  gone  1,000  metres. 

But  still  that  is  not  yet  sufficient  to  be  applied  to  all  the 
forms  of  mechanical  labour.  If,  for  example,  force  be  em- 
ployed to  displace  a  mass,  the  effort  necessary  for  the  move- 
ment will  vary  with  the  speed  which  is  given  to  that  mass. 
Let  us  imagine  a  block  of  stone  suspended  freely  at  the  end 
of  a  very  long  rope;  the  lightest  pressure  applied  to  this 
block  for  a  few  instants  will  produce  movement  in  it,  while 
the  strongest  blow  of  the  fist  will  scarcely  cause  any  sensible 
displacement,  because  the  force  requisite  to  displace  masses 
increases  according  to  the  square  of  the  speed  which  is  com- 
municated to  them.* 

A  force  of  very  short  duration  applied  to  a  mass,  produces 
only  a  shock  incapable  of  displacing  it.  But  this  same  shock, 
if  it  be  exerted  by  means  of  an  elastic  medium,  is  transformed 
into  an  act  of  longer  duration,  and  without  having  added 
anything  to  the  quantity  of  motion,  becomes  capable  of  pro- 
ducing work. 

This  elasticity  intervenes  in  the  animal  economy  to  permit 
the  utilization  of  the  very  brief  act  which  constitutes  the 
formation  of  the  muscular  wave.    The  formation  of  the  wa^e, 

*  This  action  is  expressed  by 


OF  ELECTRICITY  IN  ANIMALS. 


49 


which  lasts  only  for  some  hundredths  of  a  second,  represents 
the  time  of  application  of  each  element  of  the  force  of  the 
muscle.  At  each  new  wave,  there  would  be  produced  a  true 
ihock  if  the  elasticity  of  the  fibre  did  not  extinguish  this 
abruptness,  and  transform  these  jerky  little  contractions  into  a 
gradual  increase  of  tension  which  constitutes  the  prolonged 
effort  of  the  muscle. 

A  motor  only  works  on  the  double  condition  of  developing 
an  effort,  and  accomplishing  a  motion.  Thus  a  muscle  which 
contracts,  performs  no  external  work,  except  while  it  is  con- 
tracting; as  soon  as  it  has  reached  the  limit  of  its  contraction, 
it  ceases  to  work,  whatever  may  be  the  effort  which  it 
develops.  When  we  sustain  a  weight  after  having  lifted  it, 
the  act  of  sustainment  does  not  constitute  work. 

But,  in  these  conditions,  to  maintain  the  elastic  force  of  the 
muscle,  the  same  acts  are  produced  in  its  iuterior  as  during 
the  work ;  the  muscular  waves  succeed  each  other  at  short 
intervals,  and  heat  is  disengaged  by  chemical  action.  Now, 
this  heat,  which  cannot  transform  itself  into  action,  ought 
to  remain  in  the  muscle,  and  heat  it  strongly.  This  is  pre- 
cisely what  we  observe,  so  that  in  the  malady  called  tetanus, 
which  consists  of  a  permanent  tension  of  the  muscles,  it 
is  ascertained  that  heat  is  produced  with  an  exaggerated 
intensity,  the  temperature  of  the  entire  body  rising  several 
degrees. 

CHAPTER  VI. 

OF  ELECTRICITY  IN  ANIMALS. 

Electricity  is  produced  in  almost  all  organised  tissues— Electric  currents 
of  the  muscles  and  the  nerves — Discharges  of  electric  fishes  ;  old 
theories  ;  demonstration  of  the  electric  nature  of  this  phenomenon  — 
Analogies  between  the  discharge  of  electrical  apparatus  and  the  shock 
of  a  muscle — Electric  tetanus — Rapidity  of  the  nervous  agent  in  the 
electrical  nerves  of  the  torpedo  ;  duration  of  its  discharge 

Most  of  the  animal  or  vegetable  tissues  are  the  seat  of 
chemical  actions,  whence  result  an  incessant  disengagement 
of  electricity.     In  this  way,  the  nerves  and  muscles  of  uu 


50 


ANIMAL  MECHANISM. 


animal  furnish  manifestations  of  dynamic  electricity.  Mat- 
teucci  has  discovered  the  manner  in  which  the  muscular 
current  is  usually  produced.  Du  Bois  Reymond  has  added 
much  to  our  knowledge  of  this  current,  of  its  intensity,  and 
of  its  direction  in  every  part  of  a  muscle.  Treatises  on  phy- 
siology give  copious  details  of  experiments  relative  to  nervous 
and  muscular  electric  currents.  This  study  has  been  the 
more  eagerly  pursued  because  the  proximate  cause  of  the 
function  of  the  nerves  and  muscles  was  expected  to  be  found 
in  these  electric  phenomena. 

The  most  interesting  fact  connected  with  muscular  elec- 
tricity, with  respect  to  the  transformation  of  force,  appears  to 
be  the  disappearance  of  the  electrical  state  of  a  muscle  at  the 
moment  when  it  contracts,  or  when  it  is  tetanized.  It  appears 
then  that  the  chemical  actions  of  which  the  muscles  are  the 
seat,  are  entirely  employed  in  the  production  of  heat  and 
motion. 

To  observe  these  phenomena,  we  must  make  use  of  a  very 
sensitive  galvanometer.  Suppose  a  muscle  connected  with  one 
of  these  instruments ;  it  gives  its  currents,  and  deflects  the 
magnetic  needle  a  certain  number  of  degrees.  When  this  de- 
viation has  been  effected,  and  the  needle  has  become  stationary 
in  its  new  position,  it  is  only  necessary  to  produce  tetanus  in 
the  muscle,  and  immediately  the  needle  retrogrades  towards 
zero.  This  is  whatDu  Bois  Reymond  calls  the  negative  varia- 
tion of  the  muscular  current.  The  same  phenomenon  is 
observed  in  the  voluntary  contraction  of  the  muscles. 

The  interpretation  of  the  negative  variation  is  very  im- 
portant. Du  Bois  Reymond  having  remarked,  that  for  a 
single  muscular  shock  no  deflection  of  the  needle  from  zero  is 
obtained,  concluded  that  this  is  on  account  of  the  short  dura- 
tion of  the  electrical  disturbance  accompanying  a  shock.  In 
tetanus,  on  the  contrary,  a  series  of  modifications  in  the 
electrical  condition  of  the  muscle  correspond  to  the  series  of 
shocks  produced — their  accumulated  influence  deflects  the 
magnetic  needle. 

This  phenomenon  is  familiar  to  physicists.  It  is  known 
that  the  needle  of  a  galvanometer  subjected  to  a  frequently- 
interrupted  current,  takes  a  fixed  position  intermediate  be- 


OF  ELECTRICITY  IN  ANIMALS. 


51 


tween  zero  and  the  extreme  point  which  it  would  have  occupied 
if  the  current  had  been  continuous. 

In  the  muscles  in  which  the  shock  is  protracted,  as  in 
the  tortoise,  a  very  prolonged  change  in  the  electrical  state  is 
produced ;  and  therefore  these  muscles  can  by  each  of  their 
shocks  cause  a  deflection  of  the  magnetic  needle.  It  is  the 
same  with  the  movements  of  the  heart ;  each  of  these  appears 
to  be  only  a  shock  of  the  cardiac  muscle,  and  yet  it  deflects  the 
magnetic  needle  in  the  same  manner  as  tetanus  of  an  ordinary 
muscle.  This  fact,  that  a  negative  variation  is  equally  seen 
in  a  muscle  which  is  contracted  voluntarily,  is  of  the  greatest 
importance.  It  confirms  the  theory  which  assimilates  con- 
traction with  tetanus,  that  is  to  say,  with  a  discontinuous  or 
vibratory  action. 

One  point  which  has  been  long  under  discussion  relative 
to  the  manifestations  of  muscular  electricity,  is  whether  the 
negative  variation  is  caused  by  a  change  of  direction  in  the 
muscular  curreut,  or  by  a  transitory  suppression  of  this 
current.  The  latter  hypothesis  has  been  rendered  extremely 
probable  by  the  numerous  experiments  in  which  the  needle 
of  the  galvanometer  has  never  been  seen  to  retrograde  beyond 
the  zero  point.  Thus  the  phenomenon  of  negative  variation 
seems  to  prove  the  principle  which  we  laid  down  at  the  com- 
mencement of  this  article,  that  force  is  manifested  in  the 
muscles  in  a  different  manner  during  activity  and  repose,  and 
that  the  manifestation  under  the  form  of  mechanical  work  is 
substituted  for  that  under  the  form  of  electricity. 

Electric  fishes. — Animal  electricity  appears  in  a  much  more 
striking  form  in  the  discharges  produced  by  certain  fishes. 
In  this  case  the  special  organs  have  for  their  object  the  pro- 
duction of  electricity;  nevertheless,  by  their  structure,  their 
chemical  composition,  and  their  dependence  on  the  nervous 
system,  these  organs  remind  us  of  the  conditions  of  the  mus- 
cular apparatus. 

The  number  of  species  provided  with  electrical  organs 
which  was  formerly  restricted  to  five,*  has  been  remarkably 

*  The  five  species  formerly  known  were  the  Raya  torpedo,  the  Gynv 
notus  electricus,  the  Silurus  electricus,  the  Tetraodon  electricus,  and  the 
Trichiurus  electricus. 


52 


ANIMAL  MECHANISM. 


increased  since  Ch.  Robin  has  shown  that  all  the  species  of 
the  genus  ray  have  electrical  apparatus  and  functions  in  a 
more  or  less  rudimentary  condition.  Besides,  the  analysis 
of  this  singular  act,  which  is  called  the  electric  discharge,  has 
been  better  studied,  as  physicists  have  themselves  learned  the 
different  properties  of  the  electric  agent. 

In  the  1 8th  century,  they  said,  when  speaking  of  the  torpedo, 
that  "this  fish  when  it  is  touched  throws  out  a  kind  of 
venom  which  paralyses  and  benumbs  the  hand  of  the  fisher- 
man." Muschenbroeck,  in  the  last  century,  ascertained  the 
electrical  nature  of  the  torpedo's  discharge.  Walsh,  in  1778, 
saw  plainly  that  the  numbness  produced  by  this  animal  differs 
in  no  respect  from  that  which  is  caused  by  the  discharge  of  an 
electrical  machine.  He  proved  by  a  great  number  of  experi- 
ments, that  the  effect  produced  by  this  fish  is  manifestly 
electrical.  He  subjected  the  discharge  to  a  series  of  trials, 
in  which  it  had  the  same  effect  as  the  electricity  deve- 
loped by  machine.  For  instance,  he  showed  that  the  animal 
might  be  touched  with  impunity,  by  taking  as  a  medium  of 
communication  non-conductors  of  electricity.  Besides,  he  made 
the  discharge  pass  through  a  chain  of  individuals  holding  each 
other  by  the  hand,  and  all  felt  the  same  singular  effect  which 
is  produced  by  the  Ley  den  jar. 

At  a  later  period  Davy  obtained  with  the  current  of  the 
torpedo  the  deflection  of  the  galvanometer,  the  magnetization 
of  steel  needles  placed  within  a  spiral  of  brass  wire  traversed 
by  the  discharge,  and  the  decomposition  of  saline  solutions. 

Becquerel  and  Breschet  verified  the  same  facts  in  the  wire 
of  the  galvanometer,  the  current  circulating  from  the  back  to 
the  belly  of  the  animal. 

The  demonstration  of  the  spark  came  still  later.  Father 
Linari  and  Matteucci  obtained  this  spark  by  breaking  in 
various  ways  a  metallic  circuit  through  which  the  current  of 
the  torpedo  was  passing.  The  most  ingenious  process  is  that 
of  Matteucci,  who  made  use  of  a  file  in  the  following  manner  : 
A  metallic  plate  attached  to  a  brass  wire  is  fixed  under  the 
belly  of  the  torpedo ;  on  its  back  is  placed  a  file  on  which  the 
end  of  a  metallic  wire  rubs.  The  animal  is  then  irritated, 
and  one  or  even  several  sparks  are  seen  in  the  dark  to  pass 


OF  ELECTRICITY  IN  ANIMALS. 


53 


between  the  wire  and  the  file.  The  production  of  the  spark 
is  probably  effected  when  the  circuit  is  broken  at  the  precise 
moment  of  the  passage  of  the  torpedo's  current. 

The  use  of  the  file  is  clearly  seen,  since  the  friction 
causing  the  circuit  to  be  closed  and  broken  at  very  short 
intervals,  some  of  them  will  necessarily  coincide  with  the  dis- 
charge, as  it  has  but  a  short  duration.  Let  us  observe,  in 
passing,  that  the  production  of  two  sparks  during  the  discharge 
of  the  torpedo,  shows  very  clearly  that  it  has  an  appreciable 
duration,  measured  at  least  by  the  time  which  has  elapsed 
during  the  passage  of  the  wire  across  two  successive  teeth  of 
the  file. 

A.  Moreau  succeeded  in  collecting  this  electricity  on  a  con- 
denser which  allowed  him  to  measure  the  variation  of  the 
intensity  of  the  discharge  by  the  indications  of  a  gold  leaf 
electroscope.  We  have  seen  how  our  acquaintance  with  the 
electrical  phenomena  of  the  torpedo  has  passed  through  many 
successive  stages,  and  how  the  progress  of  physical  inquiry 
has,  on  this  subject,  invaded  the  domains  of  physiology. 

Nevertheless,  the  discharge  of  the  torpedo,  as  the  above- 
mentioned  experiments  have  shown,  seems  like  a  kind  of 
hybrid  phenomenon,  in  which  the  effects  of  tension  machines 
appear  to  be  confounded  with  those  of  a  galvanic  battery. 
We  must,  by  new  researches,  endeavour  to  assign  the  place 
in  the  series  of  well-known  manifestations  of  electricity,  which 
the  discharge  of  electric  fishes  ought  to  occupy. 

Considered  in  a  physiological  point  of  view,  this  pheno- 
menon possesses  another  kind  of  interest.  The  most  recent 
discoveries  tend  to  assimilate  the  function  of  this  electrical 
apparatus  with  that  of  a  muscle.  If,  for  example,  we  com- 
pare the  action  of  the  nervous  system  on  the  electrical  organs 
of  certain  fishes,  with  that  which  the  nerve  exercises  over  the 
muscle,  we  are  struck  with  the  following  analogies  : — 

The  electrical  discharges,  like  muscular  shocks,  can  be 
produced  under  the  influence  of  the  will  of  the  animal ;  they 
may  also  be  considered  as  reflex  phenomena;  excitation  of 
the  electric  nerve  produces  the  discharge,  as  that  of  the  motor 
nerve  produces,  the  shock  of  a  muscle  ;  an  entire  paralysis  of 
the  electrical  apparatus  takes  place  when  the  nerve  is  cut,  as 
7 


54 


ANIMAL  MECHANISM. 


in  a  muscle  when  its  nerve  is  divided.  This  paralysis  takes 
place  also  under  the  influence  of  curare,  although  this  poison 
appears  to  act  more  slowly  on  the  electric  nerves  than  on  the 
greater  part  of  the  nerves  of  motion.  Indeed,  the  electric 
tetanus,  to  employ  the  happy  expression  of  A.  Moreau,  is 
manifested,  not  only  when  the  nerve  of  the  torpedo  is  sub- 
jected to  excitations  very  rapidly  succeeding  each  other,  but 
also  when  the  animal  is  poisoned  with  strychnine  or  any 
other  tetanizing  substance. 

It  was  natural  enough  to  compare  the  different  cells  or 
laminae  of  the  electrical  apparatus  in  fishes,  with  the  elements 
of  the  voltaic  pile,  and  following  up  this  idea,  to  inquire  what 
was  the  electro-motive  power  of  each  of  these  little  elements, 
and  what  were  the  effects  of  tension  resulting  from  the 
association  of  these  pairs.  The  following  is  the  result  of  the 
experiments  of  Matteucci. 

A  portion  of  the  electrical  apparatus  of  the  torpedo,  placed 
en  rapport  with  the  extremities  of  a  galvanometer,  gives 
birth  to  a  current  of  the  same  order  as  that  in  the  apparatus 
of  which  it  formed  a  part.  The  longer  the  prism  thus 
detached,  the  more  numerous  must  be  the  elements  of  this 
kind  of  animal  pile,  and  the  greater  the  deflection  of  the  gal- 
vanometer at  the  moment  of  its  discharge ;  this  is  produced 
by  exciting  the  nervous  fibre  which  corresponds  with  the 
small  portion  of  the  electrical  apparatus  of  the  torpedo  placed 
on  the  pads  of  the  galvanometer.  Thus  far,  the  analogy  of 
the  electric  apparatus  with  the  pile  is  perfect,  since  the  effects 
of  tension  increase  with  the  number  of  elements  which  are 
employed.  This  analogy  holds  good  with  all  the  electrical 
fishes,  when  we  endeavour  to  compare  the  intensity  of  the 
currents  obtained  in  different  parts  of  the  apparatus. 

In  the  torpedo  it  is  found  that  the  discharges  are  at  their 
maximum  when  we  touch  the  two  surfaces  of  its  apparatus  on 
the  inner  side,  that  is  to  say,  at  the  thickest  part,  which  con- 
tains the  greatest  number  of  discs  superposed  on  each  other. 
In  the  gymnotus,  whose  electrical  prisms  have  so  great  a 
length,  it  is  found  that  the  discharge  is  stronger  still,  on 
account  of  the  greater  volume  and  number  of  the  elements. 
It  is  proportional  to  the  extent  of  space  contained  between  the 


OF  ELECTRICITY  IN  ANIMALS. 


55 


two  points  which  receive  this  impulse.  Id  the  sihirus  it  is 
the  same ;  a  much  greater  impression  is  made  on  us  when 
we  touch  different  points  of  the  animal  at  a  greater  distance 
from  each  other. 

In  fact,  we  may  receive  a  discharge  from  a  single  surface 
of  the  electric  apparatus  of  the  torpedo,  by  touching  unsym- 
metrical  parts,  that  is  to  say,  points  where  the  number  of 
the  elements  of  the  pile  is  not  so  great,  because  of  the 
different  length  of  the  prisms  which  compose  it.  Thus, 
although  the  polarity  may  be  identical  on  the  same  surface  of 
the  apparatus,  the  fact  of  the  inequality  of  electric  tension 
on  the  different  points  of  this  surface  suffices  to  create  the 
possibility  of  a  current,  and  to  determine  its  direction. 

As  to  the  origin  of  the  electric  force,  we  think  that  no  one 
can  now  see  anything  in  it  but  the  result  of  chemical  actions 
produced  in  the  interior  of  the  apparatus 

But  before  they  arrived  at  this  opinion,  physiologists  ad- 
vanced many  hypotheses  as  the  source  of  animal  electricity. 
Thus,  when  Du  Bois  Reymond  had  shown  that  the  nervous 
tissue  possesses  an  electro-motive  force  sufficiently  powerful, 
and  that  there  exists  in  living  nerves  a  current  in  a  constant 
direction,  it  was  thought  that  the  voluminous  nerves  which 
belong  to  the  electrical  apparatus  of  fishes  carry  electricity 
to  it,  as  the  blood-vessels  supply  blood  to  the  organs.  Mat- 
teucci  has  demonstrated  that  a  large  lobe  of  the  brain  of  the 
torpedo  is  the  origin  of  the  nerves  belonging  to  its  electrical 
apparatus.  He  has  observed  that  it  is  possible  to  remove  all 
the  rest  of  the  brain,  without  depriving  the  animal  of  the 
power  of  giving  voluntary  or  reflex  discharges  ;  but  that  it 
can  no  longer  do  so  when  this  lobe  is  destroyed.  Ho  has  for 
this  reason  named  this  the  electric  lobe  of  the  torpedo. 

When  a  dying  animal  no  longer  gave  spontaneous  dis- 
charges, it  was  sufficient,  said  Matteucci,  to  touch  the  electric 
lobe  in  order  to  obtain  discharges  more  violent  than  those 
which  the  animal  gave  voluntarily  during  the  state  of  perfect 
activity. 

Nevertheless,  the  notion  of  Matteucci  has  been  exaggerated, 
when  this  thought  was  attributed  to  him,  that  electricity  is 
formed  in  the  brain  of  the  torpedo,  and  is  conveyed  by  its 


56 


ANIMAL  MECHANISM. 


nerves.  It  is  as  much  as  to  say  that  the  motive  force  is  created 
in  the  brain  and  conveyed  to  the  muscles  by  the  nerves  of 
motion.  The  electricity  of  the  torpedo  has  its  origin  in  the 
special  organ  of  this  fish — as  mechanical  work  is  originated 
in  a  muscle.  When  we  see  the  phenomena  of  electricity 
or  of  motion  produced,  the  motive  or  electric  nerves  fulfil 
only  the  duty  of  transmitting  the  order  received  from  the 
brain ;  but  the  electricity  which  circulates  in  the  nerves  is 
not  that  which  is  manifested  so  energetically  in  the  discharge 
of  the  apparatus.  It  is,  says  Matteucci  himself,  as  if  we 
were  to  confound  the  effect  of  the  gunpowder  with  that  of 
the  priming  which  has  been  used  in  order  to  fire  the  charge. 

Thus,  the  most  probable  theory  is  that  which  assimilates 
the  electric  nerves  to  those  of  motion,  the  discharge  to  a 
muscular  shock,  the  series  of  discharges  to  tetanus. 

In  order  to  verify  this  theory,  we  have  endeavoured  to 
ascertain*  whether  the  nerves  of  the  torpedo  carry  out  the 
commands  of  the  will  with  the  same  rapidity  as  the  nerves  of 
motion ;  if,  when  the  electric  apparatus  has  received  the  order 
transmitted  by  the  nerve,  it  hesitates,  like  the  muscle,  an 
instant  before  it  re- acts  (lost  time) ;  in  fact,  whether  the  dis- 
charge of  the  torpedo,  contrary  to  those  given  by  tension 
machines,  possesses  a  certain  duration  which  may  be  compared 
to  that  of  the  shock  of  a  muscle. 

It  has  been  seen,  that  heat,  cold,  the  ligature  of  the  arteries, 
and  the  action  of  certain  poisons  modify  considerably  the  form 
and  duration  of  the  muscular  shock.  If  experiment  showed 
that  as  to  its  retardation,  its  duration,  and  its  other  phases, 
the  torpedo's  discharge  corresponds  with  the  shock  of  a  muscle; 
if  it  is  proved,  that  in  both  cases,  the  same  agents  produce  the 
same  effects,  we  should  be  right  in  assimilating  still  more 
completely  the  electrical  phenomena  with  those  of  motion ;  the 
physiology  of  the  former  would  illustrate,  in  many  points, 
that  of  the  latter. 

During  a  stay  of  a  few  weeks  at  Naples  we  have  been 
able  to  sketch  out  this  mode  of  inquiry,  which  ha*s  furnished 

*  See,  for  the  details  of  these  experiments,  ' '  Journal  de  l'anatomie  et 
de  la  physiologie."  1872. 


OF  ELECTRICITY  IN  ANIMALS. 


57 


results  as  yet  incomplete,  but  which  tend  to  assimilate  the 
electrical  with  the  muscular  action.  These  results  are  as 
follow  : — 

1 .  The  rapidity  of  the  nervous  agent  in  the  electrical  nerves 
of  the  torpedo  seems  evidently  to  be  the  same  as  that  of  the 
nervous  agent  producing  motion  in  the  frog. 

2.  The  phenomenon  called  by  Helmholtz  lost  time  exists 
also  in  the  electric  apparatus  of  the  torpedo,  and  lasts  about 
the  same  time  as  in  the  muscle. 

3.  The  discharge  of  the  torpedo  is  not  instantaneous,  like 
that  of  certain  kind  of  tension  electrical  apparatus,  but  it 
is  prolonged  about  fourteen  hundredths  of  a  second ;  which  is, 
in  a  remarkable  degree  equal  to  the  duration  of  a  shock  in  a 
frog's  muscle. 

We  cannot  enter  here  into  the  details  of  the  experiments 
which  have  furnished  these  results,  but  we  will  endeavour,  in 
a  few  lines,  to  explain  the  method  which  we  employed. 

Registering  apparatus  measure  the  slightest  intervals  of 
time  ;  this  we  have  seen  in  speaking  of  the  estimated  rapidity 
of  the  nervous  agent.  But,  in  order  to  employ  the  graphic 
method,  we  must  have  motion  to  give  the  required  signal. 

Thus,  in  the  experiment  of  Helmholtz,  the  muscular  shock 
itself  announced  that  the  order  of  movement  which  the  nerve 
had  to  convey  had  arrived  at  its  destination. 

In  order  to  obtain  the  signal  of  the  electric  discharge,  we 
have  employed  it  to  excite  the  muscle  of  a  frog,  the  shock  of 
which  was  inscribed  on  the  registering  cylinder. 

The  trace  furnished  by  the  frog- signal  is  somewhat  delayed, 
it  is  true,  after  the  excitation  has  been  produced ;  but  this 
delay  is  a  known  quantity,  and  it  can  easily  be  taken  into 
account. 

The  following  is  the  method  adopted  to  measure  with  the 
ordinary  myograph  the  duration  of  the  different  acts  which 
precede  the  discharge  of  the  torpedo. 

In  a  preliminary  experiment  (fig.  12)  the  nerve  of  the  frog 
was  directly  excited,  and  a  note  was  taken  of  the  time  (e  g) 
which  elapsed  between  the  instant  (e)  of  the  excitation,  and 
the  signal  (#)  given  by  the  frog. 

In  a  second  experiment  the  torpedo  was  excited,  still  at  the 


58  ANIMAL  MECHANISM. 

instant  (e),  and  the  electricity  of  its  discharges  was  collected 
by  means  of  conducting  wires  which  sent  it  to  the  nerve  of 
the  frog  signal.    This  would  give  its  shock  at  the  point  (t). 


Fig.  12. — Measure  of  the  time  which  elapses  between  the  excitation  of 
the  electric  nerve,  and  the  discharge  of  the  torpedo. 


The  difference  (g  t)  would  express  the  time  consumed  by 
the  torpedo  between  the  excite  tion  of  its  nerve  and  the  dis- 
charge. By  varying  the  experiment,  as  we  have  done  for  the 
motive  nerves  (page  43),  we  obtain  the  measure  of  the 
rapidity  of  the  electric  nervous  agent,  and  that  of  the  lost  time 
in  the  torpedo  apparatus.* 

Finally,  in  order  to  measure  the  duration  of  the  electrical 
action,  we  had  recourse  to  a  method  which  consists  in  col- 
lecting this  discharge  during  a  very  short  time  (1-1 00th  of  a 
second)  to  send  it  to  the  frog  signal,  and  varying  gradually  the 
instant  at  which  the  electricity  of  the  torpedo  was  collected. 
It  was  thus  ascertained  that  starting  from  the  point  (t)  one 
might,  during  14-100 ths  of  a  second,  obtain  a  series  of  signals 
from  the  frog — t' ,  t" ,  t"'}  t""f  but  that  beyond  that  time  the 
frog  gave  no  signals,  thus  proving  that  the  discharge  had 
terminated. 

We  have  not  been  able  to  follow  out  farther  the  compari- 
son of  the  electric  with  the  muscular  action ;  but,  according 
to  the  results  already  furnished  by  experiment,  we  can  foresee 

*  Deprived  of  appropriate  apparatus,  we  have  been  obliged  to  construct 
for  ourselves  a  kind  of  registering  instrument  which  should  measure  short 
intervals  of  time  with  sufficient  precision.  We  refer  the  reader,  for  the 
real  arrangement  of  the  experiments,  to  the  ' '  Journal  de  l'anatomie  et  de 
la  physiologie, "  loc.  cit.  Fig.  12  represents  tracings  which  one  would 
obtain  with  the  registering  instruments  already  known. 


ANIMAL  MECHANISM. 


59 


that  new  analogies  will  still  show  themselves  between  these 
two  manifestations  of  force  in  living  beings,  mechanical  work 
and  electricity. 


CHAPTER  VII. 

ANIMAL  MECHANISM. 

Of  the  forms  under  which  mechanical  work  presents  itself — Every 
machine  must  be  constructed  with  a  view  to  the  kind  of  work  which 
it  has  to  perform — Correspondence  of  the  form  of  muscle  with  the  work 
which  it  accomplishes — Theory  of  Borelli — Specific  force  of  muscles 
— Of  machines ;  they  only  change  the  form  of  work,  but  do  not 
increase  its  quality  —  Necessity  of  alternate  movements  in  living 
motive  powers — Dynamical  energy  of  animated  motors. 

If  we  have  lingered  long  over  the  origin  of  heat,  of 
mechanical  work,  and  of  electricity  in  the  animal  kingdom, 
it  was  in  order  to  establish  clearly  that  these  forces  are  the 
same  as  those  which  are  seen  in  the  inorganic  world.  Certain 
evident  differences  must  have  struck  the  earlier  observers,  but 
the  progress  of  science  has  shown,  more  and  more  clearly, 
this  identity,  which  is  now  disbelieved  only  by  those  whose 
minds  are  still  under  the  influence  of  obsolete  theories. 

Mechanical  force,  to  which  our  attention  must  now  be 
exclusively  directed,  has  hitherto  been  studied  only  in  its 
origin;  we  must  follow  it  through  all  its  applications  to 
work  of  different  kinds  which  it  executes  in  animal  me- 
chanism. 

In  all  the  machines  employed  in  the  arts  we  must  have 
organs  which  serve  as  media  between  the  forces  which  we 
employ  and  the  resistance  which  are  required  to  be  overcome. 
This  word  organ  is  precisely  that  which  anatomists  use  to 
designate  the  portions  which  compose  the  animal  machine. 
The  laws  of  mechanics  are  applicable  as  well  to  animated 
motors  as  to  other  machines ;  this  truth,  however,  has  to  be 
demonstrated,  but,  like  many  others,  it  was  for  a  long  time 
unrecognized. 


60 


ANIMAL  MECHANISM, 


Of  the  forms  of  mechanical  work. — When  we  have  at  our 
disposal  a  certain  quantity  of  force,  it  is  necessary,  in  order  to 
utilize  it,  to  collect  it  under  conditions  which  vary  according 
to  the  nature  of  the  effects  which  we  desire  to  produce. 

We  have  seen  that  the  measure  of  work  actually  employed 
is  the  product  of  the  resistance  multiplied  by  the  space 
through  which  it  has  to  pass.  Such  a  measure,  being  the 
product  of  two  factors,  may  remain  constant  if  the  two  factors 
vary  inversely.  So  that  a  considerable  weight,  raised  to  a 
slight  height,  will  give  the  same  result  of  work  as  a  light 
weight  raised  to  a  greater  height. 

These  will  be  two  different  forms  of  the  same  quantity  of 
work ;  but,  in  this  case,  the  form  is  of  extreme  importance. 
In  order  that  the  work  applied  should  be  available,  it  is  ne- 
cessary that  its  form  should  be  the  same  as  that  of  the 
resisting  force — that  is,  of  the  work  required  to  be  done. 

If  we  have  as  a  moving  power  a  piston  of  a  steam  engine 
of  large  diameter  and  short  length,  capable  of  lifting  100 
kilogrammes  to  the  height  of  a  centimetre,  and  that  it  is 
necessary  with  this  generator  of  force  to  lift  one  kilogramme 
to  the  height  of  a  metre,  which  equally  represents  a  kilo- 
grammetre  of  work,  the  motive  force  in  this  machine  cannot 
be  utilized  directly  ;  for  at  the  end  of  the  stroke  of  the  piston 
the  weight  of  a  kilogramme  will  only  have  been  lifted 
one  centimetre,  and  -j^-  of  the  force  at  our  disposal  will  re- 
main unemployed.  Every  machine,  therefore,  must  be  con- 
structed with  a  view  to  the  special  form  under  which  the 
resistance  to  be  overcome  presents  itself. 

It  is  true  that  by  means  of  certain  contrivances,  levers  or 
wheel-work  properly  combined,  it  is  possible  to  cause  a  cer- 
tain quantity  of  work  to  pass  from  one  form  to  another,  and 
to  apply  it  to  the  resistance  to  be  overcome.  But  this  will 
be  the  object  of  ulterior  study.  We  have  only  to  consider  at 
this  moment  the  case  in  which  the  force  is  directly  applied 
to  the  obstacle  which  it  has  to  surmount,  which  is  a  very 
frequent  condition  in  animated  motive  powers. 

Let  us  return,  then,  to  the  hypothesis  in  which  the  moving 
force  of  the  piston  of  an  engine  must  be  applied  directly  to 
overcome  resistance.    Under  these  conditions  the  constructor 


ANIMAL  MECHANISM. 


CI 


will  be  careful  to  give  to  the  surface  of  the  piston  such  an 
area,  that  the  pressure  on  this  surface  may  be  precisely  equal 
to  the  resistance  which  it  has  to  overcome ;  then  lie  will  give 
to  the  cylinder  such  a  length  that  it  will  allow  the  piston  to 
travel  just  as  far  as  the  resistance  ought  to  move.  It  is  only 
under  these  conditions  that  the  machine  will  do  the  desired 
work,  and  utilize  all  its  moving  power.  On  the  contrary, 
in  the  case  in  which  work  answering  to  a  kilogrammetre 
must  be  done  by  lifting  100  kilogrammes  to  the  height  of  a 
centimetre,  the  cylinder  must  be  made  so  large  that  the  pres- 
sure of  steam  on  the  surface  of  the  piston  will  develop  an 
effort  of  100  kilogrammes,  and  such  a  length  only  must  be 
given  to  the  cylinder,  that  the  movement  of  the  piston  may 
be  merely  a  centimetre. 

One  cannot  substitute  one  of  these  forms  of  cylinder  for 
the  other,  for  in  one  case  the  force  would  be  insufficient,  and 
in  the  other,  the  range  would  be  too  restricted. 

The  only  thing  which  is  equal  in  botli  is  the  amount  of 
work  that  the  two  machines  can  do,  that  is  to  say,  the  pro- 
duct of  the  force  employed  multiplied  by  the  space  passed 
through ;  this  is  again  the  product  of  the  surface  of  a  section 
of  the  cylinder  multiplied  by  its  length,  or,  in  other  terms, 
it  is  the  volume  of  steam  contained  in  each  machine,  this 
vapour  being  supposed  to  be  at  an  equal  tension. 

This  proportion  of  the  volume  of  the  matter  which  works 
to  the  work  performed,  is  found  in  every  case  in  which  a 
moving  force  is  employed. 

Two  masses  of  lead  falling  from  the  same  height  will  do 
work  proportionate  to  their  volume,  or,  which  is  the  same 
thing,  to  their  weight.  Two  threads  of  india-rubber  of  the 
same  length,  both  of  which  have  been  stretched  to  the  same 
degree,  will  do  work  proportionate  to  their  transverse  sec- 
tions, and,  consequently,  to  their  respective  weights.  Lastly, 
two  threads  of  the  same  diameter,  but  of  unequal  lengths, 
after  having  been  subjected  to  the  same  elongation  in  pro- 
portion to  their  original  lengths,  will,  as  they  contract,  do 
work  proportionate  to  their  respective  lengths,  that  is  to  say, 
to  their  weight. 

This  leads  to  the  consideration  of  muscle,  which  conforms 


62 


ANIMAL  MECHANISM. 


rigorously  to  the  general  laws  which  we  have  just  enunciated. 
The  larger  a  muscle  is,  that  is  to  say,  the  more  extensive  is 
its  surface,  the  more  susceptible  it  is  of  considerable  effort. 
But,  on  the  other  hand,  a  muscle  contracts  only  in  proportion 
to  its  own  length.  We  may  estimate  that  the  mean  shortening 
of  a  muscle  while  contracting,  when  it  is  not  detached  from 
the  animal,  is  about  a  third  of  its  length  when  in  repose.  It 
follows  that  the  work  done  by  a  muscle  will  be  in  proportion 
to  its  length  and  its  transverse  section ;  that  is  to  say,  to  its 
volume  or  to  its  weight. 

Thus,  it  is  possible  to  ascertain,  according  to  the  anatomi- 
cal characters  of  a  muscle,  what  is  the  force  which  it  pos- 
sesses, relatively  to  that  of  other  muscles  of  the  same  animal, 
and  what  is  the  form  under  which  its  work  is  done. 

The  substance  of  the  muscles,  that  is  to  say,  of  red  flesh, 
presents  the  same  density  in  the  different  parts  of  the  animal 
frame ;  in  consequence  of  which  the  weight  is  the  most  exact 
and  the  most  expeditious  method  of  estimating  the  relative 
importance  of  two  masses  of  muscle,  and  of  predicting  the 
quantity  of  work  which  they  are  able  to  execute. 

As  to  the  form  under  which  muscular  work  must  be  pro- 
duced, it  is  deduced  not  less  easily  from  the  form  of  the 
muscle.  If  it  be  thick  and  short,  it  should  produce  a  strong 
effect  multiplied  by  a  short  range ;  if  it  be  long  and  slender 
it  will  have  a  more  extended  range,  but  will  only  develop 
feeble  energy. 

There  are  many  examples  in  proof  of  this  law  which 
regulates  muscular  action — the  sterno-mastoidal,  the  sarto- 
rius,  and  the  rectus  abdominis,  are  muscles  of  a  long  range, 
or,  as  it  may  be  otherwise  expressed,  having  a  great  ex- 
tent of  movement ;  they  have  a  fleshy  portion  of  greater 
length.  The  large  pectoral  muscle,  the  gluteus  maximus, 
or  the  temporal  muscle  are  large  and  short  muscles,  that 
is  to  say,  capable  of  a  considerable  effort,  but  of  slight 
contraction. 

Borelli  already  understood  the  laws  of  muscular  force ; 
without  the  intervention  of  the  notion  of  work,  which  was  not 
introduced  into  mechanics  at  the  time  when  he  lived;  he 
made  a  very  clear  distinction  between  these  two  opposite 


ANIMAL  MECHANISM. 


63 


characteristics  of  the  action  of  a  muscle  according  to  the 
impulse  of  its  volume  or  its  length.  And  as  a  theory  is 
always  required  to  satisfy  the  mind,  this  author  sought  to 
interpret  these  different  effects  by  a  theory  of  the  structure  of 
the  muscles. 

Let  us  imagine,  said  he,  a  minute  chain  of  metal  formed 
of  circular  elastic  rings,  and  that  an  extensile  force  should  be 
exerted  on  this  chain.  Each  ring  will  change  its  shape  and 
assume  an  oval  form,  and  the  whole  chain  will  be  lengthened 
in  proportion  to  the  number  of  its  rings.  When  it  recovers 
itself,  under  the  influence  of  elasticity,  the  chain  will  grow 
shorter  again  in  proportion  to  its  length.  The  minute  chain 
of  Borelli  is  the  primitive  fibre  revealed  to  us  in  the  animal 
economy  by  the  microscope.  But,  said  Borelli,  if  we  form  a 
bundle  of  a  great  number  of  these  chains,  each  one  of  them 
will  resist  the  extensile  force  in  proportion  to  the  elasticity  of 
its  rings,  that  is  to  say,  the  thickness  of  the  bundles,  and  the 
force  with  which  the  extended  bundle  will  recover  itself  will 
be  in  the  same  ratio. 

We  do  not  reason  otherwise  now  that  histology  has  shown 
us,  in  a  muscle,  a  bundle  of  fibres  whose  actions  are  com- 
bined like  the  chains  suggested  by  the  Naples  professor. 

Passing  to  other  considerations,  this  author  studied  the 
influence  exerted  by  the  direction  of  the  fibres  on  the  force 
which  they  develop.  He  remarked  that  the  muscles  whose 
fibres  converge  obliquely  on  the  same  tendon,  like  the  barbs 
of  a  feather  on  the  central  shaft,  ufford  neither  a  range  nor 
an  effort  proportionate  to  their  length  and  their  sections.  We 
have  no  modification  to  make  of  this  estimate  of  the  composi- 
tion of  forces  in  the  muscular  organ. 

Of  the  specific  force  of  muscles.  —  In  the  machines  constructed 
by  man,  it  is  not  enough  to  measure  the  longitudinal  and 
transverse  dimensions  of  the  cylinder,  in  order  to  know  what 
quantity  of  work  each  stroke  of  the  piston  will  develop  ;  we 
must  also  know  under  what  pressure  the  steam  acts.  That 
is  estimated  by  the  number  of  atmospheres  it  can  lift  as  it 
escapes.  At  other  times  the  force  of  the  steam  is  measured 
by  the  number  of  kilogrammes  of  pressure  which  it  exerts  on 
every  square  centimetre  of  the  surface  of  the  cylinder.  In 


64 


ANIMAL  MECHANISM. 


every  case  it  is  an  estimate  of  the  specific  force  of  a  certain 
volume  of  steam  which  is  to  be  determined. 

In  the  same  manner,  in  hydraulic  machines,  we  must  know 
the  charge  of  water  or  its  pressure,  in  order  to  ascertain  the 
work  which  the  machine  can  perform. 

Physiologists  have  also  sought  to  determine  the  specific 
force  of  muscular  tissue  in  different  animals,  and  to  compare 
with  the  unit  of  transverse  section  of  muscle  the  effort  which 
it  can  make.  In  this  manner  they  have  estimated  that  the 
muscle  of  the  frog  would  develop  an  effort  of  692  grammes 
(E.  Weber)  for  each  square  centimetre  of  section  ;  that  human 
muscle  would  develop  1087  (Koster).  In  the  bird  the  force 
would  be  about  1200  (Marey) ;  in  the  insect  it  would  be  still 
greater  (Plateau). 

According  to  Straus  Durkheim,  a  muscle  of  the  stag-beetle 
weighing  20  centigrammes  would  carry,  if  we  measure  the 
moment  of  power  and  that  of  resistance  a  weight  of  seven 
kilogrammes. 

By  such  estimates  as  these,  we  might  compare  animated 
moving  powers  with  machines  working  under  variable  pres- 
sures. The  frog,  wt  might  say,  works  with  a  pressure  less 
than  one  atmosphere,  man  with  a  pressure  greater  than  one 
atmosphere.  There  would  be  a  greater  pressure  in  the  bird, 
and  still  greater  in  the  insect. 

Of  machines. — When  mechanical  force  cannot  be  directly 
utilized,  because  it  is  not  in  harmony  with  the  form  of  work 
which  it  ought  to  effect,  various  means  are  employed  in  the 
arts  to  transform  it.  Machinery  known  under  the  names  of 
wheels  and  levers  are  continually  used  for  this  purpose.  In 
the  animal  organism  contrivances  are  also  found  which  change 
the  form  of  the  work  of  the  muscles.  The  lever  is  almost 
exclusively  used  by  nature  for  this  purpose.  The  arrange- 
ment of  the  bony  levers  which  form  the  skeleton  is  so  generally 
known  that  it  needs  no  explanation  here ;  but  there  is  a  very 
common  error  on  this  point,  even  among  physiologists,  which 
it  is  necessary  to  point  out. 

Almost  all  the  levers  which  are  found  in  the  organism  belong 
to  the  third  order,  that  is  to  say,  where  the  muscular  force  is 
applied  between  the  fulcrum  and  the  resistance.    Under  these 


ANIMAL  MECHANISM. 


65 


conditions,  the  effort  that  can  be  developed  at  the  extremity  of 
the  lever  is  less  than  that  of  the  muscle ;  but  the  space  passed 
through  by  this  extremity  of  the  lever  is  proportionately 
increased,  so  that  the  product  of  the  force  multiplied  by  the 
distance  remains  the  same. 

Thus,  we  find  in  a  great  number  of  standard  treatises,  a 
sort  of  accusation  brought  against  nature,  for  having  entirely 
wasted  a  great  part  of  the  force  of  our  muscles  by  causing 
them  to  act  under  a  disadvantageous  leverage.  It  is  true, 
that  to  extenuate  this  fault,  they  are  willing  to  grant  that 
this  arrangement,  unfavourable  in  an  economical  point  of 
view,  gives  to  our  muscles  an  elegance  which  they  would  not 
have  possessed,  if  for  example,  a  long  muscular  band  had 
extended  from  the  sternum  to  the  wrist.  These  mechanical 
and  aesthetic  notions  ought  to  give  place  to  more  correct  ideas. 
We  must,  above  all,  remember  that  a  muscle  produces  work 
corresponding  to  its  volume  or  its  weight,  whatever  may  be* 
the  proportions  of  the  lever  to  which  it  is  attached.  The 
effect  of  the  latter  is  only  to  regulate  the  form  under  which  it 
produces  the  work,  without  adding  to  it  or  subtracting  from 
it.  An  error  of  the  same  kind  is  often  committed  in  con- 
sidering the  part  played  by  levers  made  use  of  by  man  in  his 
work.  It  often  happens  that  human  force  is  unable  to  raise 
certain  weights ;  we  have  recourse  in  these  cases  to  levers  of 
the  first  or  second  order,  in  which  we  increase  the  power  of 
the  arm  in  the  ratio  of  the  longer  to  the  shorter  arm  of  the 
lever. 

In  this  manner  wo  utilize  a  motive  force  which  could  not 
produce  external  work  if  we  endeavoured  to  bring  it  to  bear 
directly  on  the  resistance  to  be  overcome.  But  a  lever  which 
amplifies  the  force  exerted,  diminishes  as  much  the  extent  of 
the  work  produced ;  it  adds  nothing  to  the  work  executed  by 
the  motive  power. 

Before  the  notion  of  work  had  been  introduced  into 
mechanics,  and  when  it  was  not  clearly  understood  that  it  was 
impossible  to  increase  by  mechanism  the  amount  of  force  at 
our  disposal,  many  false  ideas  were  entertained  with  regard 
to  the  part  played  by  machinery.  When  we  consider  those 
gigantic  masses  of  stone  the  pyramids  of  Egypt,  or  those 
8 


66 


ANIMAL  MECHANISM. 


enormous  blocks,  called  dolmens,  which  our  forefathers 
erected  in  prehistoric  times,  it  was  admitted  that  these 
Titanic  works  pre- supposed  a  very  advanced  knowledge  of 
mechanism.  Even  now  it  would  require  an  immense  time, 
or  an  army  of  workmen,  to  execute  similar  works  by  employ- 
ing only  the  force  of  man  and  that  of  animals. 

We  must  not  imagine  that  the  old  Gauls  or  ancient 
Egyptians  were  able  to  escape  from  the  inevitable  necessity  of 
employing  many  men  or  an  enormous  lapse  of  time  in  these 
labours  at  the  period  when  the  only  source  of  mechanical 
work  was  that  derived  from  living  beings. 

But  we  live  under  new  and  better  conditions,  thanks  to 
the  invention  of  machinery  whi?h  develops  mechanical  work. 
In  addition  to  the  utilization  of  natural  motive  powers,  such 
as  water  courses  and  wind,  man  is  now  able  to  employ  steam 
engines,  by  means  of  which  a  small  quantity  of  fuel  does  the 
work  of  a  great  many  animals.  It  is  by  these  means  that 
Egypt  has  succeeded  in  a  few  years  in  cutting  through  the 
Isthmus  of  Suez,  an  enterprise  which,  four  thousand  years  ago, 
would  have  absorbed  the  efforts  of  many  generations. 

Necessity  of  alternate  motion  in  living  motive  powers. — When 
the  piston  of  a  machine  has  reached  the  end  of  its  stroke,  the 
steam  which  impelled  it  must  escape,  and  the  piston  must 
return  in  the  opposite  direction  to  accomplish  fresh  work. 
In  the  same  manner,  the  muscle,  after  having  contracted, 
must  be  relaxed  in  order  to  act  afresh.  But  mechanicians 
have  found  that  in  the  alternate  movements  there  is  a  loss  of 
work.  When  a  heavy  object  impelled  forward  with  rapidity 
has  to  be  brought  back  in  the  opposite  direction,  it  is  neces- 
sary first  to  destroy  the  work  which  it  contains,  so  to  speak, 
under  the  form  of  active  force.  Precisely  in  the  same  manner, 
when  a  limb  suddenly  extended  is  required  to  be  rapidly  bent, 
the  momentum  acquired  must  first  be  destroyed ;  to  do  which 
requires  an  expenditure  of  work. 

To  guard  against  this  loss  of  motive  power,  mechanicians 
have  recourse,  as  much  as  possible,  to  the  employment  of 
circular  movements  instead  of  motion  to  and  fro.  Thus,  man 
who  is  so  often  inspired  in  his  inventions  by  the  arrange- 
ments of  which  nature  offers  him  examples,  deviates  in  this 


ANIMAL  MECHANISM. 


67 


case  from  his  model ;  he  endeavours  to  surpass  it,  and  he  is 
right.  To  make  this  understood  we  cannot  do  better  than 
quote  a  passage  in  which  L.  Foucault  compares  the  screw- 
propeller  of  ships  to  the  organs  of  swimming  in  fishes  : — 

"  In  our  machines,"  said  he,*  "  we  have  usually  a  great 
number  of  parts  entirely  distinct  one  from  the  other,  which 
only  touch  each  other  at  certain  points  ;  in  an  animal,  on  the 
contrary,  all  the  parts  adhere  together ;  there  is  a  connection 
of  tissue  between  any  two  given  parts  of  the  body.  This  is 
rendered  necessary  by  the  function  of  nutrition  which  is 
continually  going  on,  a  function  to  which  every  living  being 
is  subject  during  the  whole  of  its  existence.  We  can,  besides, 
understand  the  absolute  impossibility  of  obtaining  a  con- 
tinued movement  of  rotation  of  one  part  on  another,  while 
still  preserving  the  continuity  of  these  two  parts." 

Thus,  a  profound  difference  separates  mechanisms  employed 
by  nature  from  those  invented  by  man ;  the  former  are  sub- 
ject to  special  requirement  from  which  the  latter  can  be  freed. 
The  muscle  can  only  act  under  the  condition  of  being  attached 
by  its  vessels  and  nerves  to  the  rest  of  the  organism.  No 
portion  of  the  body,  not  even  the  bones  themselves,  which 
have  the  least  vitality,  can  be  free  from  this  necessity. 

One  might  find,  in  the  animal  organism,  many  other 
mechanical  appliances,  the  arrangement  of  which  resembles 
that  of  machines  invented  by  man,  but  with  differences  ever 
of  the  same  kind  as  those  which  we  have  just  described. 

For  instance,  the  circulation  of  the  blood  is  effected  in  living 
beings  by  a  veritable  hydraulic  machine,  with  its  pump,  valves, 
and  pipes.  But  the  fundamental  difference  between  this 
complicated  mechanism  and  machines  constructed  by  man, 
arises  from  the  absence  of  independent  portions,  and  especially 
of  the  piston.  The  heart  is  a  pump  without  a  piston,  and  its 
variations  of  capacity  are  obtained  by  the  contractility  of 
the  coats  of  the  vessels  themselves.  With  the  exception  of 
this  difference,  we  find  perfect  analogies  between  the  circula- 
tory apparatus  of  animals  and  hydraulic  motive  powers.  The 
function  of  the  valves  is  identical  in  both  in  spite  of  apparent 
differences. 

*  "  Journal  des  Debats,"  Oct.  22,  1845. 


68 


ANIMAL  MECHANISM. 


We  have  formerly  noticed  in  the  circulation  of  the  blood  an 
influence  which  regulates  and  increases  the  effective  work  of  the 
cardiac  pump ;  it  depends  on  the  elasticity  of  the  arteries.* 
In  like  manner,  in  hydraulic  machines,  man  has  recourse  to  the 
employment  of  elastic  reservoirs,  to  utilize  more  fully  the  work 
of  pumps,  and  to  render  uniform  the  movement  of  the  liquid, 
notwithstanding  the  intermittent  character  of  the  motive 
power.  This  effect  may  be  compared  to  that  which  we  have 
before  remarked  in  the  elasticity  of  muscles. 

Dynamic  energy  of  animated  motors. — Animated  motive 
powers  and  machines  are  subject  to  the  same  estimation  of 
work ;  it  is  the  dynamic  energy  of  the  former  as  compared 
with  the  latter. 

The  production  of  external  work  corresponding  to  75  kilo- 
grammetres  per  second,  has  been  called  the  horse-power,  or, 
in  more  general  terms,  the  motive  power  of  one  horse,  it  being 
supposed  that  one  horse  could  develop  the  same  amount  of 
work. 

But  animal  motors  cannot  work  incessantly,  so  that  the 
horse-power  would  represent  at  the  end  of  the  day  a  much 
greater  amount  of  work  than  the  animal  could  have  produced, 
had  it  been  employed  as  a  motive  force. 

Man  is  estimated  much  lower  as  to  his  dynamic  energy, 
(•^q  of  a  horse-power),  and  yet,  if  we  only  require  from  the 
muscular  force  of  a  man  an  effort  of  short  duration,  it  will 
furnish  dynamic  energy  exceeding  that  of  a  horse -power.  In 
fact,  the  weight  of  a  man  is  often  more  than  75  kilogrammes  ; 
each  time  that  the  body  is  raised  to  the  height  of  a  metre 
per  second,  in  mounting  a  staircase,  the  man  has  effected 
during  this  second  the  work  adequate  to  one  horse-power. 
And  if,  during  several  instants,  he  can  give  to  his  ascent  the 
speed  of  two  metres  per  second,  this  man  will  have  developed 
the  work  of  two  horse-power. 

Thus,  in  our  estimate  of  the  work  done  by  the  greatest  or 
the  smallest  animals,  we  must  consider  it  as  a  multiple  or  a 
fraction  of  the  ordinary  measure  of  horse-power. 

*  cc  Physiologie  m^dicale  de  la  circulation  du  sang." 


ORGAN  AND  FUNCTION. 


69 


CHAPTER  VIII. 

HARMONY  BETWEEN  THE  ORGAN  AND  THE  FUNCTION. — 
DEVELOPMENT  HYPOTHESIS. 

Each  muscle  of  the  body  presents,  in  its  form,  a  perfect  harmony  with  the 
nature  of  the  acts  which  it  has  to  perform — A  similar  muscle,  in 
different  species  of  animals,  presents  differences  of  form,  if  the 
function  which  it  has  to  fulfil  in  these  different  species  is  not  the 
same — Variety  of  pectoral  muscles  in  birds,  according  to  their  manner 
of  flight— Variety  of  muscles  of  the  thigh  in  mammals,  according  to 
their  mode  of  locomotion— Was  this  harmony  pre-established? — 
Development  hypothesis— Lamarck  and  Darwin. 

The  comparison  between  ordinary  machines  and  animated 
motive  powers  will  not  have  been  made  in  vain,  if  it  lias 
shown  that  strict  relations  exist  between  the  form  of  the 
organs  and  the  characters  of  their  functions  ;  that  this  cor- 
respondence is  regulated  by  the  ordinary  laws  of  mechanics, 
bo  that  when  we  see  the  muscular  and  bony  structure  of  an 
animal,  we  may  deduce  from  their  form  all  the  characters  of 
the  functions  which  they  possess. 

It  is  known  that  the  transverse  volume  of  a  muscle  corres- 
ponds with  the  energy  of  its  action ;  that  the  athlete,  for 
instance,  is  recognized  by  the  remarkable  relief  in  which  each 
of  his  muscles  stands  out  under  the  skin.  But  less  is  known 
concerning  the  physiological  signification  of  the  length  of 
the  muscles,  that  is  to  say,  the  less  or  greater  length  of 
their  contractile  fibres.  And  yet  Borelli  has  already  given 
the  true  explanation.  In  his  opinion,  as  we  have  seen,  this 
length  of  red  fibre  is  proportioned  to  the  extent  of  movement 
which  the  muscle  is  fitted  to  produce. 

This  distinction  between  the  contractile  or  red  fibre  and 
the  inert  fibre  of  the  tendon  is  of  the  utmost  importance. 
Experiment  has  shown  that  the  muscles  when  they  contract 
are  shortened  to  an  extent  which  represents  a  constant  frac- 
tion of  their  length.  We  may,  without  erring  from  the  truth, 
estimate  at  ^  of  their  length,  the  extent  to  which  a  muscle 


70 


ANIMAL  MECHANISM. 


can  contract.  But,  whatever  may  be  the  absolute  value  of 
this  contraction,  it  is  always  in  proportion  to  the  length  of 
red  fibre  ;  that  is  the  result  of  the  nature  of  the  phenomena 
which  produce  work  in  the  muscle. 

Thus,  every  muscle  whose  two  points  of  attachment  are 
susceptible  of  being  much  displaced  by  the  effect  of  contrac- 
tion, must  necessarily  be  a  long  muscle.  On  the  contrary, 
every  muscle  which  has  to  produce  a  movement  of  short 
extent  must  of  necessity  be  a  short  muscle,  whatever  may  be 
the  distance  which  separates  the  two  points  of  attachment. 
Thus,  the  flexors  of  the  fingers  and  toes  are  short  muscles ; 
but  they  are  furnished  with  long  tendons,  which  convey  even 
to  the  phalanges  of  the  fingers  or  toes  the  slight  movement 
originated  at  a  considerable  distance  at  the  fore-arm  or  the  leg. 

It  is  easy  to  estimate,  in  the  dead  body,  the  extent  of  the 
displacement  which  a  muscle  can  exercise  on  its  two  points  of 
attachment.  By  producing  the  movements  of  flexion  or 
extension  in  a  limb,  we  can  ascertain  with  sufficient  exact- 
ness the  extent  by  which  they  separate  or  draw  together  the 
osseous  attachments  of  its  muscles.  In  a  recent  skeleton  we 
can  also  judge  with  sufficient  accuracy  of  the  amount  of  these 
movements  by  the  extent  to  which  the  articulated  surfaces 
can  glide  over  each  other. 

In  examining  the  muscular  frame  of  man  we  are  struck 
with  the  extreme  length  of  the  sartorius  muscle ;  it  is  easy 
to  be  seen  that  no  other  can  displace .  to  such  an  extent  its 
points  of  bony  attachment.  The  sterno-mastoidal  and  the 
magnus  rectus  abdominis  are,  after  this,  the  longest  muscles ; 
these  also  are  muscles  which  have  very  extensive  movements. 
We  might  thus  cause  all  the  muscles  of  the  organism  to  pass 
under  review,  and  in  them  all  we  should  see  that  the  length 
of  the  red  fibres  corresponds  with  the  extent  of  the  movement 
which  this  muscle  has  to  execute.  But,  in  the  study,  we 
must  be  on  our  guard  against  a  cause  of  error  which  would 
tend  to  arrange  certain  short  muscles  among  those  which  are 
longer. 

Borelli  himself  has  noticed  this  cause  of  error;  he  has 
shown  how  penniform  muscles,  that  is  to  say,  those  whose 
fibres  are  inserted  obliquely  into  the  tendon,  like  the  barbs  of 


ORGAN  AND  FUNCTION. 


71 


a  feather  into  the  common  shaft,  are  short  muscles  which 
appear  like  long  ones.  These  considerations  are  indis- 
pensable when  we  wish  to  understand  the  action  of  the 
various  muscles  of  the  organism ;  it  is  only  by  this  means 
that  we  can  estimate  the  real  length  of  their  contractile  parts. 

Though  the  harmony  between  the  form  and  the  function  of 
different  muscles  is  revealed  everywhere  in  the  anatomy  of  the 
human  frame,  this  harmony  becomes  much  more  striking  if 
we  compare  with  each  other  different  species  of  animals. 
Comparative  anatomy  shows  us,  in  species  closely  allied  to 
each  other,  a  singular  difference  in  the  form  of  certain 
muscles  whenever  the  function  of  these  muscles  varies.  Thus, 
in  the  kangaroo,  essentially  a  leaping  animal,  we  find  an 
enormous  development  of  the  muscles  of  leaping,  the  glutei, 
the  triceps  extensor  cruris,  and  the  gastrocnemial  muscles. 

In  birds  the  function  of  flight  is  exercised  under  very  dif- 
ferent conditions  in  different  species ;  so,  also,  the  anatomical 
arrangement  of  the  muscles  which  move  the  wing,  the  pectoral 
muscles,  varies  in  a  very  decided  manner  in  different  species. 
To  show  the  perfect  harmony  which  exists  between  the  func- 
tion and  the  organ,  it  would  be  necessary  to  enter  into  long 
details  of  the  mechanism  of  flight.  The  reader  will  find, 
farther  on,  explanations  on  this  head.  We  will  content  our- 
selves with  giving  in  a  few  words  the  differences  which  have 
been  observed  in  the  movements  of  the  wing,  and  in  the  form 
of  the  muscles  which  produce  them. 

Every  one  has  remarked  that  birds  which  have  a  large 
surface  of  wing,  as  the  eagle,  the  sea-swallow,  &c,  give  strokes 
of  only  a  slight  extent ;  that  depends  on  the  great  resistance 
which  a  wing  of  so  large  a  surface  meets  with  in  the  air. 

Birds,  on  the  contrary,  which  have  but  very  little  wings, 
move  them  to  a  great  extent,  and  thus  compensate  for  the 
slight  resistance  which  they  meet  with  from  the  air;  the 
guillemot  and  the  pigeon  belong  to  the  second  group.  If  it 
be  admitted  that  the  first-mentioned  birds  must  make 
energetic  but  restricted  movements,  and  that  the  second  must 
move  with  less  energy,  but  with  greater  amplitude  of  stroke, 
the  conclusion  arrived  at  must  necessarily  be  that  the  first 
ought  to  have  large  and  short  pectoral  muscles,  while  in  the 


72  ANIMAL  MECHANISM. 

second,  these  muscles  should  be  long  and  slender.  This  is 
precisely  what  takes  place  ;  we  can  be  assured  of  this,  by  the 


Fig.  13.— Skeleton  of  a  flamingo  (after  Alph.  Milne-Edwards)  ;  the  wing 
is  very  large,  the  sternum  very  short  and  deep,  which  indicates  the  size 
and  the  shortness  of  the  pectoral  muscles. 


ORGAN  AND  FUNCTION. 


7-'5 


simple  inspection  of  the  sternum  in  different  species ;  for 
this  bone  measures,  in  some  degree,  the  length  of  the  pectoral 
muscles  which  are  lodged  in  its  lateral  cavities.  Thus,  birds 
with  long  wings,  havo  a  wide  and  short  sternum ;  the  others 
have  one  which  is  long  and  slender. 


Fig.  14.  —  Skeleton  of  a  penguin  :  sternum  very  lung,  wing  very  short. 


The  comparison  of  homologous  muscles  in  mammals  of 
different  kinds  is  not  less  instructive  under  the  aspect  in 
which  we  are  now  considering  them.  But  one  is  often  em- 
barrassed in  this  comparison  by  the  difficulty  of  recognizing 
the  homology.    The  discrepancies  are  sometimes  so  striking 


n 


ANIMAL  MECHANISM. 


that  anatomists  have  described  under  various  names  the  same 
muscle  in  different  species. 

Still,  in  the  greater  number  of  cases,  the  homology  is  not 
doubtful ;  it  is  implicitly  admitted  by  the  fact  of  an  identical 
designation  being  applied  to  certain  muscles  in  different 
species.  These  are  precisely  the  muscles  which  we  shall  take 
for  an  example,  to  show  the  harmony  which  exists  between 
the  function  and  the  organ. 


Fig.  15. — Skeleton  of  the  wing  and  sternum  of  the  sea-swallow  (Hirundo 
marina)— showing  the  extreme  shortness  of  the  sternum,  and  the  great 
length  of  the  wing. 


Thus  the  femoral  biceps  is  easily  recognized  in  all  mam- 
mals ;  and  it  varies  considerably,  especially  in  its  lower  attach- 
ment. In  certain  quadrupeds  it  is  inserted  all  along  the  leg, 
almost  to  the  heel ;  in  these  animals  the  leg  is  never  ex- 
tended upon  the  thigh ;  in  animals  which  have  the  power  of 
leaping,  the  lower  attachments  of  the  biceps  is  more  elevated  ; 
it  is  still  more  so  in  the  simise,  which  can  almost  extend 
the  leg  upon  the  thigh  and  stand  upright.    In  man  the  biceps 


ORGAN  AND  FUNCTION. 


75 


is  inserted  high  in  the  perinaeum.  If  one  can  rely  on  the 
anatomical  plates  of  Cuvier  and  of  Laurillart,  the  negro  has 
the  perinaeal  insertion  of  the  biceps  not  so  high  as  in  the 
white  man,  thus  approximating  to  its  position  in  the  ape. 

Neglecting  at  present  the  question  why  there  should  be 
this  variety  in  the  attachment  which  regulates  the  motion  of 
the  biceps,  let  us  content  ourselves  with  considering  the  con- 
sequences which  this  arrangement  may  have  upon  its  function. 
It  is  clear  that  during  the  movement  of  the  flexion  and  ex- 
tension of  the  knee,  each  portion  of  the  bone  describes  around 
this  articulation  an  arc  of  a  circle  which  is  larger  as  it  recedes 
from  the  centre  of  motion.  It  is  equally  evident  that  each  of 
these  points  will  move  to  a  greater  or  less  distance  from  the 
femur  or  the  ischium,  according  to  the  extent  of  the  circular 
movement  which  it  executes.  And  as  great  movements  should 
correspond  with  long  contractile  fibres,  we  ought  to  find 
inequalities  in  the  length  of  the  biceps  in  different  mammals. 

This  is  precisely  what  is  observed.  In  man,  whose  biceps 
has  its  lower  insertion  very  near  the  knee,  the  extent  of  the 
movements  of  the  moveable  attachments  is  not  very  consider- 
able, so  the  contractile  fibre  will  have  relatively  little  length, 
while  the  tendon  will  occupy  a  certain  part  of  the  extent  of 
the  biceps.  In  the  ape,  the  inferior  attachment  of  the  muscle 
taking  place  lower  down  will  consequently  have  greater  mo- 
bility; whence  the  necessity  of  a  greater  length  of  active 
muscle,  which  is  effected  by  the  tendinous  part  being  shorter. 
In  quadrupeds  the  tendon  of  the  biceps  almost  entirely  dis- 
appears, and  the  muscle  is  formed  of  red  fibre  throughout 
almost  all  its  extent. 

The  rectus  internus  muscle  of  the  thigh  presents  the  same 
variability  in  its  attachments  and  its  structure.  If  we  observe 
its  arrangement  in  man  (fig.  16),  we  see  at  once  that  the 
attachment  of  this  muscle  to  the  leg  is  very  near  the  knee, 
and  that  its  tendon  is  very  long.  Let  us  examine  the  same 
muscle  in  an  ape  (figs.  17  and  18),  we  find  that  its  tibial 
attachment  is  much  farther  from  the  knee,  and  as  a  conse- 
quence of  the  more  extended  movements  which  this  attachment 
executes,  we  find  that  the  muscular  fibre  gains  length  at  the 
expense  of  that  of  the  tendon,  which  is  extremely  short. 


76 


ANIMAL  MECHANISM. 


This  variability  in  the  point  of  attachment  is  still  very 
noticeable  in  the  semi-tendinosus  muscle,  which  derives  its 
name  from  the  fact  that  in  man,  about  half  of  the  length 


Fig.  16.— Muscles  of  tlie  thigh  in  man.  The  sartorius  muscle  (above)  and 
the  rectus  interims  (below),  are  darkly  shaded,  that  they  may  be  more 
easily  recognized.  The  rectus  internus  is,  at  its  lower  extremity,  pro- 
vided with  a  long  tendon ;  its  fleshy  part  is  short,  which  is  in  harmony 
with  the  slight  extent  of  movement  in  this  muscle,  the  attachment  of 
which  is  very  close  to  the  knee.  The  sartorius  muscle  is  provided  with 
a  short  tendon  at  its  inferior  attachment. 

of  the  muscle  is  occupied  by  the  tendon.  In  fact,  the  inferior 
attachments  of  the  semi-tendinosus  in  man  is  very  close  to  the 
articulation  of  the  knee,  but  in  apes,  where  it  is  attached 
lower  down,  the  muscle  has  almost  entirely  lost  its  tendon ; 
it  is  altogether  lost  in  the  greater  part  of  other  mammals,  in 
the  Coaita,  for  example. 


ORGAN  AND  FUNCTION. 


77 


We  might  multiply  indefinitely  examples  which  prove  the 
perfect  harmony  between  the  form  of  the  muscles  and  the 
characters  of  their  functions.  Everywhere  the  transverse 
development  of  these  organs  is  associated  with  strength,  as 
in  the  triceps  of  the  kangaroo,  or  the  masseters  of  the  lion  • 


Fig.  17.— Muscle  of  the  thigh  in  the  Magot  ;  rectus  internus  muscle  almost 
entirely  formed  of  red  fibres  ;  the  attachments  of  this  muscle  being  at 
a  considerable  distance  from  the  knee,  give  it  a  great  extent  of  move- 
ment in  bending  the  leg  upon  the  thigh,  tiartorius  muscle,  haviug  a  very 
short  tendon. 


everywhere  also,  the  length  of  muscle  is  connected  with  the 
extent  of  movement,  as  in  the  examples  which  we  have  just 
cited. 

Is  this  harmony  pre-established,  or  rather  is  it  formed  under 
the  influence  of  function  in  different  creatures  ?    In  the  same 
manner  as  we  see  the  muscles  increase  in  volume  by  the 
habit  of  employing  energetic  efforts ;  we  also  observe  them, 
9 


78 


ANIMAL  MECHANISM. 


under  the  influence  of  more  extended  movements,  acquire  a 
greater  length  ?  Can  we  see  a  displacement  of  the  tendinous 
attachments  of  the  muscles  to  the  skeleton,  under  the  influence 
of  changes  in  the  force  of  muscular  traction  ?  Such  is  the  second 
problem  which  we  propose  to  ourselves,  and  which  experiment 
should  be  called  on  to  determine. 


Fig.  18.— Muscles  of  the  thigh  of  the  Coaita  Rectus  interims,  inserted 
at  a  distance  from  the  knee,  almost  entirely  without  tendon.  The 
sartorius  having  its  superior  attachment  very  far  from  the  coxo-femoral 
articulation,  has  very  extended  movements  ;  it  possesses  in  consequence 
a  great  length  of  red  fibre,  and  not  of  tendon. 

THE   DEVELOPMENT  THEORY. 

The  natural  sciences  have  derived  at  the  present  day  a 
great  impulse  from  the  influence  of  the  ideas  of  Darwin.* 


THE  DEVELOPMENT  THEORY. 


79 


Not  that  the  opinions  of  the  illustrious  Englishman  are  yet 
universally  accepted ;  it  has  been  recently  seen  with  what 
vehemence  the  defenders  of  the  prevalent  theory  reject  the 
development  hypothesis.  But  the  appearance  of  the  Darwinian 
theory  has  excited  long  discussions ;  to  the  arguments  which 
Lamarck  formerly  brought  forward  in  favour  of  the  vari- 
ability of  living  beings,  many  others  have  been  added  by  the 
partizans  of  development.  On  the  other  side,  the  old  doctrine 
has  been  maintained  with  a  passion  which  was  little  antici- 
pated, so  that  at  the  present  day,  naturalists  are  divided  into 
two  camps ;  almost  all  who  have  devoted  themselves  to  the 
study  of  zoology  or  of  botany  have  taken  one  side  or  the  other. 

In  one  of  these  camps  we  find  that  the  old  school,  those 
who  consider  the  organized  world  almost  unchangeable,  have 
retrenched  themselves.  According  to  them,  the  very  numerous 
series  of  animals  and  plants  is  limited  to  a  certain  number  of 
species,  unalterable  types  which  have  the  power  of  transmit- 
ting themselves  through  successive  generations,  from  their 
origin  to  the  end  of  time.  It  is  scarcely  admitted  that  the 
species  has  the  power  of  departing  even  slightly,  and  in  a 
temporary  manner,  from  the  primitive  type.  Those  slight 
changes,  which  are  brought  about  by  variations  of  climate  or 
of  food,  by  domestication,  or  some  other  disturbing  force  of  the 
same  order  pass  away  when  the  species  is  again  placed  under 
the  normal  conditions  of  its  existence.  The  primitive  type 
then  re-appears  in  its  original  purity. 

In  the  other  camp  the  belief  is  entirely  different ;  the  living 
being  is  incessantly  modified  by  the  medium  which  it  inhabits, 
the  temperature  which  it  finds  there,  and  the  nourishment 
which  it  procures.  The  habits  which  it  is  forced  to  assume 
in  order  to  live  under  new  conditions  cause  it  to  acquire 
special  aptitudes  which  modify  its  organism,  and  change  the 
form  of  its  body.  And  because  hereditary  descent  transmits 
to  descendants,  within  certain  limits,  the  modifications  acquired 
by  their  ancestors,  the  species  is  modified  by  degrees.  Lamarck 
was  the  author  of  this  theory  of  development,  to  which  Darwin 
and  his  followers  have  recalled  the  attention  of  naturalists. 
Darwin  adds  to  these  external  influences,  which  can  modify  the 
species  of  animals,  another  cause  which  maintains  and  increases 


80 


ANIMAL  MECHANISM. 


these  modifications  continually,  when  they  are  advantageous 
to  the  species.    This  cause  is  natural  selection. 

If  the  chances  of  birth  have  given  to  certain  individuals  a 
slight  modification  which  renders  them  stronger  or  more 
active,  as  the  case  may  be,  but  altogether  more  fitted  to  main- 
tain the  struggle  for  existence,  these  individuals  are  destined  by 
that  very  circumstance  to  reproduce  their  kind.  Not  only  does 
their  physical  superiority  increase  their  chance  of  longevity,  and 
give  them  by  that  means  more  time  to  multiply,  but,  according 
to  Darwin,  the  very  existence  of  a  physical  superiority  in  an 
animal  causes  it  to  be  preferred  above  others,  for  the  purpose 
of  reproduction.  Thus  the  entire  species  would  be  improved 
by  successive  acquisitions  of  new  qualities  every  time  that  an 
individual  happened  to  be  born  with  better  endowments  than 
the  other  representatives  of  this  species. 

The  struggle  between  the  old  school  and  that  of  development 
threatens  to  endure  yet  a  long  time,  without  either  side  finding 
a  victorious  argument  to  overcome  the  other.  Every  one 
knows  the  reasons  which  have  been  alleged  on  both  sides,  and 
for  which,  in  their  turn,  geology*  archaeology,  zoology,  and 
agriculture  have  been  laid  under  contribution.  When  and 
how  will  the  strife  end  ?  No  one  can  as  yet  answer  this  ques- 
tion. Yet,  if  one  might  venture  a  prediction  as  to  the  issue 
of  the  combat,  founded  on  the  actual  attitude  of  the  adverse 
parties,  one  might  predict  the  defeat  of  the  old  school.  Their 
ranks  are,  in  fact,  thinned  every  day ;  they  evidently  grow 
discouraged,  and  seem  to  avow  their  inability  to  furnish  proofs 
of  -a  scientific  character,  by  sheltering  themselves  under  an 
orthodoxy  that  has  nothing  in  common  with  the  dispute. 

One  objection  might  perhaps  be  brought  against  both 
systems — that  of  keeping  too  much  to  generalities  in  their 
discussions,  and  not  bringing  sufficiently  into  relief  the  promi- 
nent points  of  the  debate. 

Thus,  we  must  allow  that  Lamarck  is  much  too  vague  in 
his  explanations,  when  he  attributes  to  outward  circumstances 
the  changes  in  the  living  organism.  Between  a  need  which 
is  manifested  and  the  appearance  of  a  form  of  organ  which 
corresponds  to  that  need,  there  is  a  hiatus  which  his  theory 
has  not  filled.    He  tells  us  that  the  animal  species  which  we 


DEVELOPMENT  THEORY, 


SI 


now  see,  so  admirably  adapted,  each  to  the  kind  of  life  which 
it  leads — provided,  according  to  their  necessities,  with  claws 
or  hoofs,  wings  or  fins,  sharp  teeth  or  horny  beaks — have 
not  always  lived  under  this  form  ;  that  they  have  gradually 
acquired  these  diverse  conformations,  which  are  at  present  in 
perfect  harmony  with  the  conditions  under  which  they  live. 
But,  when  we  ask  him  to  show  us  a  modification  of  this  kind 
in  process  of  accomplishment  under  an  external  influence,  the 
author  of  the  "Philosophie  Zoclogique"  has  little  wherewith 
to  furnish  us,  except  modifications  of  slight  importance ;  he 
objects  that  scientific  observation  does  not  go  far  enough  back 
into  the  ages  of  the  world.  If  we  open  the  tombs  of  Mem- 
phis and  show  Lamarck  the  skeletons  of  animals  identical 
with  those  which  live  in  Egypt  at  the  present  day,  he  replies 
without  being  disconcerted:  "It  is  because  these  animals 
lived  under  the  same  conditions  as  those  whicli  exist  at  the 
present  time."  The  answer  is  as  good  as  the  attack,  but 
proves  nothing.  We  might  carry  on  the  discussion  for  ever 
ou  such  grounds  as  these. 

Darwin  is  more  precise  when  he  pleads  in  favour  of  natural 
selection.  There  is  no  one  at  the  present  time  who  does  not 
admit  the  enormous  power  of  selection  in  modifying  the  type 
of  organized  beings.  Breeders  have  produced  the  most 
curious  transformations  in  the  animal  kingdom,  by  choosing 
continually  for  the  purpose  of  reproduction,  individuals  pos- 
sessing in  a  high  degree  the  physical  characteristics  which 
they  desire  to  impress  on  the  race.  Selection  produces  in  the 
vegetable  kingdom  transformations  of  a  similar  kind  ;  so  that 
Darwin  has,  without  giving  way  too  much  to  hypothesis, 
attributed  the  principal  part  in  transformation  to  a  selection 
which  is  made  naturally,  for  the  reasons  that  have  just  been 
given.  But  Darwin,  as  well  as  Lamarck,  only  considers  under 
a  restricted  point  of  view  the  causes  of  the  transformation  of 
organized  beings.  Each  of  the  two  chiefs  of  this  doctrine 
gives  the  greatest  prominence  to  the  cause  of  variation  which 
he  first  has  pointed  out. 

The  new  school  which,  by  a  judicious  eclecticism,  endea- 
vours to  make  a  due  partition  between  these  two  kinds  of 
influences,  in  order  to  explain  by  successive  transformations 


82 


ANIMAL  MECHANISM. 


the  surprising  variety  of  living  beings,  has  already  furnished 
important  arguments  in  favour  of  development.  But  many 
savants  look  with  suspicion  on  these  studies;  they  consider 
that  the  immutability  and  variability  of  animal  species  belong 
to  the  domain  of  insoluble  questions. 

It  is  true,  that  if  we  ask  the  partizans  of  development  to 
prove  experimentally  the  reality  of  their  doctrine ;  if  we 
require  of  them,  for  example,  to  transform  the  ass  species  into 
the  horse  or  anything  analogous  to  it,  they  are  forced  to  avow 
their  inability,  and  they  reply  that  it  is  necessary,  in  order 
to  effect  this,  to  exercise  modifying  influences  during  millions 
on  millions  of  years.  It  must  indeed  have  been  by  very  slow 
transitions  that  the  variation  of  species  has  been  effected,  if  it 
indeed  has  taken  place.  Consequently,  in  the  absence  of  an 
experimental  solution,  the  development  hypothesis  can  neither 
be  proved  nor  refuted. 

Learned  men,  whose  minds  are  habituated  to  rigorous  de- 
monstration, are  not  interested  in  such  questions ;  they  have 
no  scientific  value  in  their  estimation.  And  yet  science  meets 
with  such  every  day.  "When  an  astronomer  studies  the  in- 
fluences which  may  cause  the  heavenly  bodies  to  move  more 
slowly ;  when  he  predicts  a  modification  of  the  orbit  of  the 
earth  after  the  lapse  of  some  millions  of  years,  or  a  lengthen- 
ing of  the  period  of  rotation  of  our  planet — changes  which 
would  affect  all  the  inhabitants  of  the  earth  with  a  mortal 
chill — this  philosopher  is  listened  to.  When  he  speaks  of  a 
cause,  however  slight  it  may  be,  of  the  retardation  of  a 
planetary  movement,  every  one  understands  that  if  this  cause 
should  continue  during  many  ages,  its  effects  will  be  exag- 
gerated by  the  lapse  of  time.  No  one  tells  this  astronomer 
to  wait  till  some  millions  of  years  have  proved  the  accuracy  of 
his  reasonings. 

Why  should  we  be  more  unjust  to  the  theory  of  develop- 
ment ?  It  cannot,  it  is  said,  bring  before  our  eyes  the  trans- 
formation of  one  animal  into  another.  This  is  true,  but  it 
may  show  us  some  tendency  to  this  transformation.  However 
slight  it  may  be,  yet  accumulating  more  and  more  during 
many  ages,  it  may  become  as  complete  a  transformation  as 
we  can  imagine. 


DEVELOPMENT  THEORY. 


83 


But  what  we  have  a  right  to  demand  of  the  advocates  of 
development,  even  now,  is  that  they  should  show  us  this 
tendency ;  that  they  should  bring  it  before  us  under  the  form 
of  a  slight  variation  in  the  anatomical  characters  of  individuals 
when  exposed  to  certain  influences,  which  continued  from 
generation  to  generation,  would  in  the  end  produce  the  most 
important  modifications  in  the  species.  No  one  denies  that 
the  morphological  characteristics  of  individuals  are  transmitted 
in  different  degrees  to  their  descendants.  The  point  which 
is  to  be  demonstrated  is  the  manner  in  which  an  external 
cause  acts  in  order  to  impress  on  the  organism  the  primary 
modification.  Researches  of  this  kind  belong  to  experimental 
physiology,  and  this  science  may  even  now  furnish  us  with 
some  reliable  arguments. 

At  the  time  when  Lamarck  lived,  scientific  logic  was  not 
very  exact  in  its  requirements.  In  his  opinion,  a  want  which 
was  felt,  originated  the  organic  conformation  suited  to  satisfy  it. 

A  certain  bird  which  was  in  the  habit  of  seeking  its  food 
at  the  bottom  of  the  water,  made  constant  efforts  to  lengthen 
its  neck,  and  its  neck  grew  longer ;  another  bird  wished  to 
advance  as  far  as  possible  into  the  waters  of  a  pond  without 
wetting  its  plumage  ;  the  efforts  which  it  made  to  extend  its 
legs  gradually  gave  them  the  proportions  observed  in  the 
wading  birds  (Grallatores) .  The  giraffe,  attempting  to  feed 
on  the  foliage  of  trees,  gained  by  this  exercise  cervical  vertebrae 
of  a  surprising  length. 

Lamarck,  certainly,  attributed  to  hereditary  descent  the 
function  of  accumulating  continually  for  the  profit  of  the 
species  that  which  each  individual  had  acquired  for  his  own 
benefit  ;  but  he  did  not  show  what  the  slight  acquisition 
was  which  was  made  by  the  individual  himself,  under  the 
influence  of  external  circumstances,  and  of  the  habits  which 
he  was  forced  to  acquire.  J.  Hunter  reasoned  in  a  similar 
manner  in  sciences  of  a  different  order.  When  he  wished  to 
explain  the  cicatrization  of  wounds  and  the  consolidation 
of  fractured  bones,  he  recognized  the  necessity  that  new  tissue 
should  be  supplied  by  the  blood  ;  but  why  did  the  blood 
carry  these  elements  to  the  parts  which  needed  them  ?  "It 
was,"  said  he,  "  in  virtue  of  the  stimulus  of  necessity." 


84 


ANIMAL  MECHANISM. 


We  seek  at  the  present  day  to  state  with  precision  the  rela- 
tion  between  causes  and  effects,  to  ascertain  the  gradual  transi- 
tions which  the  animal  or  vegetable  organism  is  able  to  pass 
through  when  it  finds  itself  placed  under  new  conditions. 
We  have  a  glimpse  of  the  influence  which  function  exercises 
over  the  organ  itself  which  produces  it.  The  short  and  pithy 
formula  of  Mons.  J.  Guerin,  "Function  makes  the  organ"  ex- 
presses in  a  general  manner  the  modifying  action  of  function. 
This  formula  will  acquire  additional  force  when  supported  by 
individual  examples. 

It  must  be  shown  how  the  bones,  the  articulations,  the 
muscles  are  modified  in  various  ways  by  the  effect  of  func- 
tions of  different  kinds ;  how  the  digestive  apparatus,  yielding 
to  very  varying  kinds  of  food,  passes  through  transformations 
which  adapt  it  to  new  conditions ;  how  a  change  effected  in 
the  circulatory  function  produces  in  the  vascular  system  cer- 
tain anatomical  modifications  which  may  be  predicted  before 
they  take  place  ;  how  the  senses  acquire  new  qualities  by 
exercise,  or  lose  by  desuetude  their  former  powers.  These 
changes  of  function  under  the  influence  of  the  function  itself 
are  accompanied  by  anatomical  modifications  in  the  apparatus, 
physiologically  modified. 

The  first  demonstration  to  be  furnished  will  be  to  ascertain 
one  of  these  transformations,  and  to  show  that  it  is  always 
produced  in  a  certain  manner  under  certain  circumstances. 
And  if,  in  the  second  phase  of  the  experiment,  it  can  be 
proved  that  hereditary  descent  transmits  even  the  least  part 
of  the  modification  thus  acquired,  the  development  theory  will 
be  in  possession  of  a  solid  starting-point. 

This  seems  to  be  the  true  course  to  follow,  if  we  desire  to 
obtain  a  solution  of  this  important  question.  During  several 
years  serious  efforts  have  been  made  in  this  direction.  Having 
been  ourselves  for  a  long  time  conversant  with  the  problems 
of  animal  mechanism,  we  have  often  been  induced  to  reflect 
on  the  reciprocal  relations  of  the  organs  of  locomotion  and  of 
their  functions.  We  will  therefore  attempt  to  show  how  the 
skeleton  and  the  muscular  apparatus  harmonize  with  the 
movements  of  each  animal  under  the  ordinary  conditions  of  its 
existence. 


CHAPTER  IX. 


VARIABILITY  OF  THE  SKELETON. 

Reasons  which  have  caused  the  skeleton  to  be  considered  the  least  variable 
part  of  the  organism— Proofs  of  the  yielding  nature  of  the  skeleton 
during  life  under  the  influence  of  the  slightest  pressure,  when  long  con- 
tinued—Origin  of  the  depressions  and  projections  which  are  observed 
in  the  skeleton —Origin  of  the  articular  surfaces — Function  rules  the 
organ. 

Any  one  who  examines  the  skeleton  of  an  animal,  and  holds 
in  his  hands  its  osseous  portions  as  hard  as  a  stone  ;  who  knows 
how  these  bones  have  survived  the  destruction  of  all  the  other 
organs,  and  how  they  can  remain,  after  the  lapse  of  thousands 
of  ages,  the  only  vestiges  of  extinct  animals,  may  naturally  look 
upon  the  skeleton  as  the  unchangeable  part  of  the  organism. 
This  skeleton,  he  argues,  is  the  framework  of  the  body,  and 
the  soft  parts  are  grouped  around  it  as  best  they  may,  reposing 
in  its  cavities,  spreading  over  its  surfaces,  but  always  obey- 
ing a  law  stronger  than  their  own,  and  arranging  themselves 
in  the  spaces  which  have  been  allotted  to  them  among  the  dif- 
ferent portions  of  the  bony  structure. 

The  observer,  however  little  he  may  be  acquainted  with 
anatomy,  soon  perceives  on  the  surface  of  the  bone  a  thousand 
curious  details ;  he  sees  there  numerous  small  hollows,  little 
abodes  which  seem  to  have  been  destined  to  receive  or  to  shelter 
some  organ  that  has  disappeared.  These  hollows  correspond 
with  the  origin  of  the  muscles  which  adhered  at  these  points  to 
the  excavated  bones.  Elsewhere  there  are  deep  rounded  grooves 
which  remind  one  of  the  channels  found  in  the  curbstones  of 
ancient  wells.  A  cord  has  also  passed  in  that  direction  ;  it  was 
the  tendon  of  a  muscle  which  incessantly  glided  along  that  bone. 
But  at  the  two  extremities  of  this  humerus  the  bone  is  polished 
as  if  by  friction  ;  in  the  upper  part  it  is  rounded  like  a 
sphere,  and  it  is  lodged  in  a  cavity  of  the  shoulder-blade  which 
it  exactly  fits.    One  would  say  that  the  movement  of  these 


86 


ANIMAL  MECHANISM. 


bones  had  worn  the  surfaces  smooth  ;  the  humerus  continually 
changing  its  position,  and  turning  upon  its  axis,  seems  to 
imitate  the  action  we  employ  when  we  wish  to  obtain  by 
means  of  friction  a  body  of  a  spherical  form. 

It  is  thus,  for  instance,  that  opticians  produce  the  forms 
and  the  polished  surfaces  of  convex  and  concave  lenses.  At 
its  lower  end  the  shoulder-bone  shows  the  trace  of  the  same 
phenomenon,  a  small  spherical  projection  articulating  it  with 
the  radius ;  it  shows  also  that  there  existed  movements  of 
two  kinds,  and  close  by,  we  meet  with  a  surface  cut  like 
the  groove  of  a  pulley ;  this,  in  fact,  only  contributed  to  the 
flexion  and  extension  of  the  fore-arm. 

If  we  examine  the  skull  we  meet  with  fresh  surprises ;  here 
every  want  is  foreseen.  Deep  cavities  lodge  in  their  interior 
the  brain  and  the  organs  of  sense. 

The  nerves  have  conduits  which  allow"  them  to  pass  through ; 
each  vessel  creeps  along  a  furrow  which  forms  a  canal  for  it, 
and  is  ramified  with  the  minute  arteries  whose  rich  foliation  it 
delicately  traces  out. 

If  the  bone  were  not  so  hard,  one  would  really  suppose  that 
it  had  been  subjected  to  external  force,  of  which  it  bears,  as  it 
were,  the  impression.  But  it  is  in  vain  to  press  a  bony  sur- 
face ;  it  resists  absolutely  the  force  which  is  applied  to  it.  It 
is  necessary  to  use  a  saw  or  a  gouge  if  we  wish  to  make  a 
channel  in  it.  How  could  the  pressure  of  soft  parts  hollow 
out  these  cavities  which  are  sometimes  so  deep  ? 

The  foresight  of  nature  has  prepared  everything  in  the 
skeleton  so  that  it  may  be  disposed  in  the  best  possible  manner 
to  receive  the  organs  to  which  it  offers  its  solid  and  invari- 
able support.  Such  is  the  natural  argument  of  all  those 
who  have  not  seen,  with  their  own  eyes,  these  osseous  changes 
take  place,  and  these  channels  hollowed  out.  The  anatomist 
as  well  as  the  zoologist  have  necessarily  reasoned  in  this 
manner'  They  have  considered  the  skeleton  as  the  unalterable 
element  of  the  organism,  and  therefore  they  have  derived  from 
it  the  greater  part  of  the  specific  characters  in  zoology. 

It  must  be  very  difficult  to  oppose  an  opinion  which  has 
been  for  a  long  time  received.  Thus,  when  Mons.  Charles 
Martin,  carrying  out  and  rectifying  the  ideas  of  Vic.  d'Azir, 


VARIABILITY  OF  THE  SKELETON. 


87 


has  shown  that  the  humerus  of  a  man  or  of  an  animal  is  the 
houiologue  of  the  femur,  but  of  a  femur  twisted  on  its  axis,  so 
that  the  knee  turned  behind  becomes  an  elbow,  zoologists 
have  replied  that  this  torsion  was  purely  virtual.  Instead  of 
being  the  effect  of  a  muscular  effort,  whose  slow  and  gradual 
action  has  reversed  the  axis  of  the  bone,  this  singular  form 
is;  in  their  opinion,  the  result  of  a  pre-established  arrange- 
ment of  the  organism;  for  the  embryo  shows  a  contorted 
humerus,  before  muscular  action  has  been  sufficiently  developed 
to  produce  such  a  modification  of  its  skeleton. 

We  might,  with  greater  show  of  reason,  argue  in  a  directly 
opposite  manner. 

No  one  denies  at  the  present  day  that  the  bony  system  is 
perfectly  yielding  in  its  character.  These  organs,  which  are 
so  compact  and  so  hard  in  the  dead  skeleton,  are,  on  the  con- 
trary, essentially  capable  of  being  modified  while  the  organism 
is  living.  If  we  exert  upon  a  bone  a  pressure  or  a  tension, 
however  slight  it  might  be,  yet  if  prolonged  for  a  considerable 
time,  it  can  produce  the  strangest  changes  of  form ;  the  bone 
is  like  soft  wax  which  yields  to  all  external  forces ;  and  we 
may  say  of  the  skeleton,  reversing  the  proposition  to  which  we 
have  just  alluded,  that  it  is  completely  under  the  influence  of 
the  other  organs,  and  that  its  form  is  that  which  the  soft  parts 
with  which  it  is  surrounded  permit  it  to  assume. 

We  are  indebted  to  medicine  and  surgery  for  the  knowledge 
of  important  facts,  of  which  many  examples  could  easily  be 
given.  Thus,  when  an  aneurism  of  the  aorta  is  developed, 
and  it  happens  to  meet  in  its  course  the  sternum  or  the  clavicle, 
it  does  not  stop  at  this  barrier,  of  bone,  but  perforates  it 
in  a  few  months.  The  substance  of  the  bone  is  absorbed  and 
disappears  under  the  pressure  of  the  aneurism;  it  certainly 
resists  less  the  effort  of  the  invading  tumour  than  do  the  softer 
parts — the  skin,  for  example. 

But  this  pressure  of  the  aneurism  differs  in  no  respect 
from  that  of  the  arterial  blood;  the  force  with  which  the 
aneurismal  sac  compresses  and  perforates  the  bones,  is  present 
in  every  part  where  an  artery  touches  a  bone.  The  same  ab- 
sorption of  the  bony  material  still  goes  on,  so  that  the  artery 
hollows  out  for  itself  a  furrow  in  which  it  lodges  with  its  dif- 


88 


ANIMAL  MECHANISM. 


ferent  branches,  an  example  of  which  is  seen  in  the  internal 
surface  of  the  parietal  bones  of  the  human  skull.  Even  a  vein 
is  able  to  form  a  considerable  hollow  in  a  bone.  The  ab- 
normal dilatation  of  those  veins  which  are  called  varicose,  and 
which  is  usually  produced  in  the  legs,  is  accompanied  with  a 
change  of  form  in  the  anterior  surface  of  the  tibia  ;  the  bone 
wears  the  impress  of  the  dilated  veins.  We  cannot  say  that 
these  osseous  furrows  enter  into  the  pre-established  plan  of 
nature ;  that  the  skeleton  had  originally  these  furrows  in 
order  to  provide  for  the  swollen  state  which  should  hereafter 
be  produced.  Surgeons  know  that  these  hollows  are  formed 
in  the  bone  of  an  adult,  which  was  in  a  perfectly  normal  state 
before  accident  had  caused  the  varicose  dilatation  of  the  veins. 

It  is  a  similar  mechanism  which  forms  along  the  bones  the 
furrows  imprinted  by  the  muscles,  and  which  gives  to  the 
perinseum,  for  instance,  the  prismatic  form  by  which  it  is 
characterized. 

The  hollows  in  which  the  tendons  are  lodged  are  not  formed 
beforehand  in  the  skeleton ;  it  is  the  presence  of  the  tendon 
which  has  hollowed  them  out,  and  which  still  maintains  them. 
Should  a  luxation  take  place  and  change  the  position  of  the 
bone  with  respect  to  the  tendon,  the  former  furrow  which  is 
now  empty  is  gradually  effaced  ;  at  the  same  time  a  new 
furrow  is  formed,  and  by  degrees  assumes  the  necessary  depth 
to  allow  the  tendon  to  repose  in  its  fresh  place. 

But,  it  may  be  said,  that  the  articular  surfaces,  so  perfect 
in  their  structure,  so  well  adapted  to  the  movements  which 
they  carry  on,  are  certainly  organs  formed  beforehand.  Here 
the  bony  surfaces  are  clothed  with  a  polished  cartilage 
moistened  with  a  synovial  fluid  which  facilitates  their  move- 
ment still  more ;  all  around  them,  fibrous  ligaments  prevent 
the  bones  from  passing  the  limits  allotted  to  them,  and  the 
surfaces  from  separating  from  each  other.  So  perfect  an  ap- 
paratus could  not  be  formed  by  the  function  alone. 

We  have  here  at  least  a  proof  of  the  foresight  of  nature 
and  of  the  wisdom  of  her  plans. 

Let  us  turn  once  more  to  surgery,  which  will  show  us  that 
after  dislocations,  the  old  articular  cavities  will  be  obliterated 
and  disappear,  while  at  the  new  point  where  the  head  of  the 


VARIABILITY  OF  THE  SKELETON. 


89 


bone  is  actually  placed,  afresh  articulation  is  formed,  to  which 
nothing  will  be  wanting  in  the  course  of  a  few  mouths,  neither 
articular  cartilages,  synovial  fluid,  nor  the  ligaments  which 
retain  the  bones  in  their  place.  Here  again,  according  to  the 
expression  which  we  used  just  now,  function  has  produced 
the  organ. 

So  much  for  the  furrows  formed  in  the  bone.  But  how 
can  we  attribute  to  external  influences  those  decided  promi- 
nences which  we  observe  everywhere  on  the  surface  of  the 
skeleton,  those  apophyses,  as  they  are  called,  to  which  each 
muscle  is  attached. 

The  answer  is  not  less  easy  ;  it  is  sufficient  to  account  for 
the  formation  of  projections  on  the  face  of  the  bone,  if  we  call 
into  play  an  influence  contrary  to  that  which  we  know  to  be 
capable  of  hollowing  out  the  indentations.  We  must  admit 
that  traction  has  been  exercised  on  the  portion  of  the  bone 
where  the  projection  is  observed. 

The  existence  of  traction  on  all  the  points  in  the  skeleton  to' 
which  muscles  are  attached  is  absolutely  evident ;  it  is  clear 
that  the  intensity  of  these  tractions  is  proportional  to  the  force 
of  the  muscles  which  produce  them.  Thus,  it  is  precisely  in 
the  tendinous  attachments  of  the  stronger  muscles  that  we  find 
the  more  projecting  apophyses ;  a  proof  that  the  prominences 
in  the  bone  are  intimately  connected  with  the  intensity  of  the 
effort  acting  upon  them.  The  right  arm,  more  frequently  used 
than  the  left,  acquires  more  decided  projections  on  its  bony 
structure.  When  paralysis  of  a  limb  suppresses  the  action  of 
the  muscles,  its  skeleton  is  no  longer  under  the  influence  of 
muscular  power,  and  the  apophyses  become  less  prominent ; 
in  fact,  if  paralysis  dates  from  birth,  the  bone  remains  nearly 
in  its  foetal  form,  which  function  has  not  supervened  to 
modify. 

Comparative  anatomy  also  confirms  this  general  law  that 
the  longer  the  apophysis  is,  the  greater  energy  it  reveals  on 
the  part  of  the  muscle  which  was  inserted  into  it. 

Mons.  Durand  de  Gros  has  clearly  shown  the  influences  of 
muscular  function  on  the  form  of  the  torsion  of  the  humerus 
in  different  species  of  fossil  and  recent  animals.  Thus  the 
humerus  in  the  mole,  the  ant-eater,  and  several  other  burrow- 
10 


90 


ANIMAL  MECHANISM. 


ing  animals  is  scarcely  recognizable,  so  thickly  is  it  studded  with 
ridges  and  projections,  each  of  which  gave  insertion  to  a 
powerful  muscle. 

The  skull  and  the  lower  jaw  in  the  carnivora  bear  the  traces 
of  a  powerful  muscular  action.  In  the  skull  a  deep  hollow 
retains  the  impression  of  enormous  temporal  muscles  ;  all 
around  the  temporal  depression,  decided  ridges  were  the  solid 
points  of  attachment  of  the  muscle;  again,  a  strong  and  long 
apophysis  by  the  side  of  the  lower  jaw  shows  the  violent 
tractile  force  to  which  it  has  been  subjected  in  the  efforts  of 
mastication. 

If  the  effects  of  muscular  actions  on  the  bones  augment  with 
the  intensity  of  the  force  of  the  muscles,  they  do  not  vary  less 
in  proportion  to  the  duration  of  their  action.  From  infancy 
to  old  age,  the  modification  of  the  skeleton  goes  on  more  and 
more,  and  even  allows  us,  to  a  certain  degree,  to  determine 
the  age  of  the  subject. 

Mons.  J.  Guerin  has  shown  that  in  the  old  man  the  verte- 
brae have  longer  apophyses,  the  ribs  more  angular  curves,  &c. 
Compare  the  cranium  of  a  young  gorilla  with  that  of  an  adult 
animal ;  the  form  will  appear  to  you  so  different  that  unless 
you  had  been  told  that  the  two  skulls  belonged  to  animals  of 
the  same  species,  you  would  scarcely  have  believed  it.  Of  a 
rounded  form  in  the  young  gorilla,  it  changes  its  shape  in 
the  adult ;  it  assumes  a  kind  of  ridge  like  the  crest  of  a 
helmet ;  this  is  the  apophysis  into  which  the  temporal  muscles 
are  inserted.  We  should  never  finish  if  we  were  to  point 
out  all  the  modifications  to  which  the  skeleton  is  subjected 
in  different  species  of  animals  ;  .  modifications  which  from  the 
beginning  to  the  end  of  life  become  more  and  more  marked. 

Medicine,  in  its  turn,  furnishes  us  with  curious  information 
as  to  these  questions,  by  showing  us  the  sudden  development 
of  accidental  apophyses  which  are  called  exostoses.  In  certain 
maladies  which  attack  the  entire  body,  we  see  the  skeleton 
covered,  in  a  great  number  of  points,  with  accidental  osseous 
projections;  and  almost  all  these  prominences  are  developed  at 
the  points  of  attachment  of  the  muscles,  and  as  they  increase, 
they  extend  especially  in  the  direction  in  which  muscular 
traction  is  applied. 


VARIABILITY  OF  THE  SKELETON. 


91 


The  curvature  of  the  hones,  or  their  contortion  on  their 
axis,  is  a  phenomenon  which  is  frequently  observed.  I  have 
mentioned  that  Mons.  Ch.  Martin  has  demonstrated  that  in 
all  the  mammalia,  the  humerus  is  a  contorted  femur,  whose 
axis  has  made  half  a  turn  upon  itself ;  this  contortion,  accord- 
ing to  Gegenbaiier,  is  less  in  the  foetus  than  in  the  infant, 
and  becomes  still  more  marked  in  process  of  age.  It  is 
therefore  partly  effected  by  causes  which  are  in  action  during 
life ;  and  if  it  be  true  that  every  foetus  brings  into  the  world 
a  contorted  humerus,  it  is  not  less  true  that  this  form  may 
be  considered  as  the  effect  of  muscular  action  accumulated 
from  generation  to  generation  in  terrestrial  mammals. 

Articular  surfaces  are  particularly  interesting  to  study  when 
we  wish  to  ascertain  the  influence  of  function  over  the  organs. 
If  we  admit  that  the  friction  of  these  surfaces  lias  polished 
them,  and  given  them  their  curvature,  it  is  easy,  when  we 
consider  the  movement  which  takes  place  in  each  articulation, 
to  foresee  the  form  which  these  surfaces  ought  to  possess. 

The  surfaces  whose  curvature  has  the  greater  number  of 
degrees,  will  correspond  with  the  more  extensive  movements. 
Moderate  movements,  on  the  contrary,  will  only  produce  sur- 
faces whose  curvature  will  correspond  with  an  arc  of  but  few 
degrees.  As  a  necessary  consequence,  the  radius  of  curvature 
in  the  articular  surfaces  will  be  very  short,  if  the  move- 
ments are  very  extended ;  it  will  be  very  long  if  the  movement 
is  moderate. 

Let  us  examine,  from  this  point  of  view,  the  articulations 
of  the  foot  in  man  ;  we  see  in  the  tibio-tarsal  articulation  a 
curvature  of  small  radius,  on  account  of  the  considerable  move- 
ment of  the  foot  on  the  leg.  In  the  tarsus  the  radius  of  the 
curvature  increases  in  proportion  as  the  mobility  of  the  bones 
diminishes.  The  scaphoid  shows  articular  surfaces  of  a  great 
radius;  the  radius  increases  still  more  in  the  tarso-metat;irs;J 
articulations,  in  which  the  movements  are  very  limited  ;  then 
it  diminishes  again  in  the  articulations  of  the  metatarsals 
with  the  phalanges,  and  of  the  phalanges  with  each  other,  at 
which  point  there  is  great  mobility. 

Everyone  knows  that  if  the  articular  movement  is  only 
effected  in  one  direction)  the  surfaces  will  curve  only  in  that 


92 


ANIMAL  MECHANISM. 


direction  ;  such  are  the  trochlear  surfaces,  of  which  the  articu- 
lation of  the  elbow,  the  condyles  of  the  jaw,  &c,  are  examples. 
But  if  the  movement  is  executed  in  two  directions  at  once, 
the  surfaces  will  present  a  double  curvature,  and  in  the  case 
of  an  inequality  in  the  amplitude  of  the  movements,  the  radii 
of  these  curvatures  will  be  unequal.  Thus,  in  the  wrist  there 
exist  movements  of  flexion  and  extension  which  are  consider- 
ably extensive,  but  the  lateral  movements  are  restricted.  The 
result  of  this  is  that  in  the  elliptical  head  formed  by  the 
carpal  bone,  there  is  a  curvature  of  small  radius  in  the  direc- 
tion of  the  movements  of  flexion  and  extension,  while,  in  the 
lateral  direction,  the  curvature  belongs  to  a  circle  of  much 
greater  radius. 

It  is  still  more  interesting  to  observe  the  articular  surfaces 
of  a  series  of  animals  in  different  classes  and  species. 
Similar  articulations  present  movements  of  very  different  kinds, 
which  must  bring  about  no  less  important  differences  in  the 
articular  sui  faces. 

Let  us  take,  for  example,  the  head  of  the  humerus,  and 
follow  the  changes  of  its  form,  in  man,  in  the  ape,  the  carni- 
vora,  the  herbivora,  the  birds.  We  shall  see  that  the  perfect 
equality  of  movement  in  every  direction  which  can  be  exe- 
cuted by  the  human  arm  corresponds  with  a  perfect  sphericity 
to  the  head  of  the  humerus — that  is  to  say,  a  curvature  of  the 
same  radius  in  every  direction.  Among  apes,  those  which  in 
walking  throw  a  part  of  their  weight  usually  on  their  anterior 
limbs,  have  the  head  of  the  humerus  flattened  at  the  upper 
part,  as  if  by  the  weight  of  the  body.  Besides  this,  the 
movements  which  are  required  in  walking  being  more  ex- 
tended, the  curvature  of  the  head  of  the  humerus  in  these 
animals  presents  its  least  radius  in  the  antero-posterior  direction. 
This  modification  is  more  marked  still  in  the  carnivora,  and 
above  all  in  the  herbivora,  the  head  of  whose  humerus,  flat- 
tened above,  presents  its  short  radius  of  curvature  in  the 
direction  of  the  movements  which  serve  for  walking,  and 
which  predominate  in  this  articulation. 

Birds  possess,  in  the  articulation  of  the  shoulder,  two 
movements  of  unequal  extent.  One,  by  which  they  spread 
and  fold  their  wings,  and  which  carries  the  elbow  sometimes 


VARIABILITY"  OF  THE  SKELETON. 


93 


near  to  the  body,  and  sometimes  very  forward ;  the  other, 
usually  more  restricted,  is  made  in  a  direction  perpendicular 
to  the  former ;  it  is  that  which  constitutes  the  stroke  of  the 
wing. 

Curvatures  of  different  radii  correspond,  therefore,  to  these 
two  movements  of  unequal  amplitude  ;  to  the  greater  move- 
ment of  stretching  and  folding  the  wdng  a  curvature  of  short 
radius  corresponds ;  to  the  less  extensive  movement  which 
raises  and  lowers  the  wing  during  flight,  there  is  a  corre 
sponding  curved  surface  of  very  long  radius.  The  result  of 
this  is  that  the  head  of  the  humerus  in  birds  assumes  the 
form  of  a  very  elongated  ellipse,  at  the  level  of  the  articular 
surface. 

But  the  movements  of  flight  present  in  different  species 
great  variations  of  amplitude.  Birds  which  have  sail-like 
wings  give  but  very  small  strokes  with  them,  while  the 
pigeon,  at  the  moment  when  it  takes  flight,  strikes  its  wings 
one  against  the  other  above  and  below,  producing  a  clapping 
noise,  which  is  familiar  to  every  one. 

To  these  variations  in  the  extent  of  the  movements  corre- 
spond varieties  of  surface  in  the  head  of  the  humerus,  which 
in  birds  with  sail-like  wings  lias  a  very  elongated  elliptical 
surface ;  but  in  the  pigeon  it  tends  to  the  circular  form,  and 
very  nearly  attains  it  in  the  spheniscus,  an  aquatic  bird  found 
in  southern  seas,  and  closely  resembling  the  penguin. 

From  all  this  we  may  gather,  that  in  the  form  of  the  bony 
structure,  everything  bears  the  trace  of  some  external  influ- 
ence, and  particularly  of  the  function  of  the  muscles.  There 
is  not  a  single  depression  or  projection  in  the  skeleton, 
the  cause  of  which  cannot  be  found  in  an  external  force, 
which  has  acted  on  the  bony  matter,  either  to  indent  it,  or 
draw  it  forward.  It  was  not,  therefore,  a  metaphorical  exag- 
geration to  say,  that  the  bone  is  subject,  like  soft  wax,  to  all 
the  changes  of  form  which  external  forces  tend  to  impress 
upcn  it;  and  that,  notwithstanding  its  extreme  hardness,  it 
resists  less  than  the  most  supple  tissues  the  efforts  which  tend 
to  change  its  form. 

And  will  this  new  form,  acquired  by  means  of  function, 
disappear  with  the  individual  ?    Will  he  not  transmit  even 


94 


ANIMAL  MECHANISM. 


the  slightest  trace  to  his  descendants?  Will  hereditary 
descent  make  an  unique  exception  with  respect  to  these  ac- 
quired characters  ?  This  appears  very  improbable,  and  yet 
we  must  admit  it,  if  we  negative  the  development  theory. 
We  must  bring  forward  a  contrary  hypothesis,  which  would 
reverse  the  ordinary  laws  of  hereditary  descent,  if  we  refuse 
to  certain  anatomical  characters  the  power  of  becoming  trans- 
missible. 

VARIABILITY   OF  THE   MUSCULAR  SYSTEM. 

We  have  stated  that  the  bony  system  is  subject  to  external 
influences,  and  especially  to  those  of  the  muscles,  which  im- 
press on  each  bone  the  form  which  we  observe  in  it.  The 
great  variety  of  forms  in  the  skeletons  of  different  animal 
species  corresponds,  therefore,  with  the  diversity  of  their 
muscular  systems.  Thus,  whenever  in  animals  of  different 
species  we  find  resemblances  in  certain  bones,  we  may  affirm 
that  the  muscles  which  were  attached  to  these  bones  were 
also  similar.  Whenever  we  observe  in  an  animal,  on  the 
contrary,  a  bone  of  a  peculiar  form,  we  may  feel  assured  of 
a  peculiarity  in  the  muscles  which  were  attached  to  it. 

But  if  the  muscle  and  the  bone  vary  simultaneously,  what 
can  be  the  cause  which  influences  them  both  ?  It  is  under- 
stood that  the  skeleton,  as  it  is  modified,  plays  a  passive  part ; 
that  it  is  subject  to  the  form  imposed  upon  it  by  the  muscle. 
But  what  gives  to  the  muscle  itself,  an  organ  eminently  active, 
and  the  true  generator  of  the  mechanical  force  by  which 
the  skeleton  is  in  some  degree  modified,  the  particular  form 
which  is  revealed  to  us  by  anatomy  ? 

We  hope  to  demonstrate  that  the  power  to  which  the  mus- 
cular system  is  subjected  belongs  to  the  nervous  system.  The 
nature  of  the  acts  which  the  will  commands  the  muscles  to 
perform,  modifies  the  muscles  themselves,  in  their  volume  and 
their  form,  so  as  to  render  them  capable  of  performing  these 
acts  in  the  best  possible  manner.  And,  as  this  necessity 
which  determines  all  the  actions  of  animal  life,  governs  the 
will,  it  is  this,  which,  according  to  the  external  conditions 
under  which  every  living  being  is  placed,  influences  its  form, 


VARIABILITY  OF  THE  MUSCULAR  SYSTEM.  95 


and  regulates  it  according  to  the  laws  which,  we  must  now 
endeavour  to  make  known. 

Nothing  in  the  organic  form  is  under  the  dominion  of 
chance.  The  specific  varieties  of  living  beings  have  been  too 
often  compared  to  the  fancies  of  an  architect,  who,  while 
adhering  to  an  uniform  plan,  invents  a  thousand  varieties  of 
details,  as  a  musician  composes  a  series  of  variations  on  a 
given  theme. 

In  our  present  inquiry  we  may  say  that  the  great  variety 
which  is  found  in  the  muscular  apparatus,  whether  in  the 
different  parts  of  the  body  of  an  animal,  or  in  the  homologous 
parts  of  animals  of  different  species ;  for  instance,  varieties 
in  the  volume  or  the  length  of  muscles;  the  very  unequal 
partition  of  the  red  contractile  fibre,  and  the  inert,  white, 
glistening  fibre  of  the  tendon  ;  that  all  this  is  entirely  subject 
to  the  dynamic  laws  of  muscular  function. 

Adaptation  of  the  form  of  muscles  to  the  requirements  of  function. 
Normal  anatomy  can  only  furnish  us  with  examples  of  the 
harmony  which  exists  between  the  form  of  the  organs  and 
their  habitual  function.  Experiment  alone  can  show  us  that, 
by  changing  the  function,  we  may  bring  into  the  form  of  the 
organs  modifications  which  may  harmonize  them  with  the 
new  conditions  which  may  be  imposed  upon  them.  It  will 
be  easy  to  make  experiments  for  this  purpose.  From  the 
moment  when  we  know  in  what  direction  the  modification 
ought  to  be  produced,  in  order  to  adapt  the  organ  to  the 
function,  the  changes  effected  in  animals  placed  by  us  under 
conditions  of  peculiar  muscular  function,  will  derive  an  im- 
portant significance.  But  while  we  wait  for  the  realization  of 
this  vast  series  of  experiments,  there  are  some  which  we  can 
employ  even  now.  Experiments  made  ready  to  our  hand  are 
furnished  by  pathological  anatomy. 

Medicine  and  surgery  are  full  of  information  on  this  in- 
teresting subject.  They  show  us,  for  example,  that  it  is 
movement  itself  which  keeps  up  the  existence  of  the  muscle. 
A  long  repose  of  this  organ  brings  about  first  the  diminution 
of  its  volume,  and  soon  a  change  in  the  elements  which  com- 
pose it.  Fatty  corpuscles  are  substituted  for  the  striated  fibre 
which  form  its  normal  element;    at  last,  these  corpuscles, 


96 


ANIMAL  MECHANISM. 


becoming  more  and  more  abundant,  invade  the  entire  sub- 
stance of  the  muscle.  This  phase  of  alteration,  or  fatty  dege- 
neration, is  followed  by  an  absorption  of  the  substance  of  the 
muscle,  which  disappears  entirely  at  the  end  of  a  certain 
time. 

Thus,  not  only  does  the  volume  of  the  organ  increase  or 
diminish  according  as  the  necessities  of  its  habitual  function 
require  a  greater  or  less  force,  but  it  wholly  disappears  when 
its  function  is  entirely  suppressed.  This  effect  is  observed  in 
paralysis,  where  all  nervous  action  is  destroyed ;  in  certain 
cases  of  dislocation,  which  bring  closer  together  the  two  inser- 
tions of  a  muscle,  so  as  to  render  its  action  useless  ;  sometimes 
even  in  fracture  and  anchyloses,  which,  by  an  abnormal  con- 
nection, render  the  two  extremities  of  a  muscle  immovable, 
and  prevent  any  contraction  of  its  fibres. 

But  wdiat  will  happen,  if  the  muscle,  instead  of  losing  all 
its  function,  only  experiences  a  change  with  respect  to  the 
extent  of  the  movements  which  it  can  execute  ?  After  certain 
incomplete  anchyloses,  or  certain  dislocations,  we  see  the 
articulations  lose  more  or  less  of  their  movements;  as  the 
muscles  which  command  flexion  and  extension  only  need,  in 
such  cases,  a  part  of  the  ordinary  extent  of  their  contraction. 

If  the  theory  just  enunciated  be  correct,  these  muscles  ought 
to  lose  a  portion  of  their  length.  In  order  to  verify  this  fact, 
we  have  only  to  make  a  short  excursion  into  the  domain  of 
pathological  anatomy. 

A  warm  discussion  arose,  some  twenty  years  ago,  as  to  the 
transformation  which  the  muscles  underwent  in  those  patients 
who  were  afflicted  with  the  deformity  commonly  known  by  the 
name  of  club  foot.  Sometimes  the  foot  is  twisted  upon  the 
leg,  so  that  the  surface  which  should  be  uppermost  is  next 
the  ground ;  sometimes  the  foot  is  so  forcibly  extended  that 
the  patient  walks  continually  on  its  extremity.  In  all  these 
cases  the  muscles  of  the  leg  have  only  a  very  limited  play  ; 
they  undergo,  therefore,  either  fatty  or  fibrous  transformation. 
Among  these  muscles,  those  which  have  no  longer  any  action 
undergo  fatty  degeneration,  and  then  disappear ;  while  those 
whose  action  is  partly  preserved,  present  only  a  change  as  to 
the  proportion  of  red  fibre  and  tendon.    In  the  latter  case 


VARIABILITY  OF  THE  MUSCULAR  SYSTEM.  97 


the  oontractile  substance  diminishes  in  length,  and  is  re- 
placed by  tendon,  which  often  assumes  a  considerable  develop- 
ment. 

J.  Guerin,  when  pointing"  out  the  fibrous  degeneration  of 
the  muscles,  thought  that  he  saw  in  it  the  proof  of  a  primi- 
tive muscular  retraction,  which  would  ultimately  have  pro- 
duced dislocation  of  the  foot.  This  eminent  surgeon  also 
thought  that  the  alteration  of  the  fibre  was  the  only  lesion  of 
the  muscles  in  club-foot.  Scarpa  maintained,  on  the  contrary, 
that  in  the  greater  number  of  cases  the  luxation  of  the  foot 
was  the  original  phenomenon. 

As  to  the  nature  of  muscular  change,  all  surgeons  at  present 
ogree  in  admitting  that  it  may  have  two  different  forms,  and 
that  sometimes  the  muscle  undergoes  fatty  degeneration,  and 
in  other  cases  it  is  transformed  into  fibrous  tissue.  We  are 
especially  indebted  to  the  beautiful  works  of  Cuvier,  for  our 
knowledge  of  the  conditions  under  which  each  of  those 
changes  in  the  muscular  substance  is  produced. 

An  example  will  illustrate  how  the  muscles  are  affected 
according  as  their  function  is  suppressed,  or  simply  limited 
in  extent. 

The  muscles  of  the  calf  of  the  leg,  or  gastrocnemians,  aro 
two  in  number;  their  attachments  and  their  functions  are 
very  different.  Both  are  inserted  below  in  the  calcaneum,  by 
the  tendon  of  Achilles,  and  are,  consequently,  extensors  of  the 
foot  on  the  leg.  But  their  superior  insertions  are  different ; 
the  solens,  having  its  insertion  exclusively  in  the  bones  of  the 
leg,  has  no  other  office  than  that  of  extending  the  foot,  as  we 
have  said  before.  The  twin  gastrocuemii,  on  the  contrary, 
being  inserted  in  the  femur,  above  the  condyles  of  that  bone, 
have  a  second  function,  that  of  bending  the  leg  upon  the 
thigh. 

Let  us  suppose  that  anchylosis  of  the  foot  has  been  pro- 
duced; it  entirely  suppresses  the  function  of  the  soleus,  which 
passes  through  the  fatty  degeneration,  and  disappears.  The 
two  gastrocnemii  are  in  a  different  condition ;  if  their  action 
on  the  foot  has  ceased,  there  still  remains  their  function  of 
bending  the  leg  on  the  thigh ;  these  muscles  have,  therefore, 
only  one  of  their  movements  reduced  in  amplitude.  Con- 


98 


AMMAL  MECHANISM, 


sequently,  under  such  conditions,  the  twin  muscles  lose  only 
a  part  of  the  length  of  their  fibres ;  they  undergo  what  sur- 
geons call  partial  fibrous  transformation,  a  modification  which 
is  only  a  change  of  proportion  between  the  red  fibre  and  the 
tendon. 

Those  who  are  accustomed  to  regard  pathology  as  a  com- 
plete infraction  of  physical  laws,  will  perhaps  be  astonished 
to  see  us  search  among  these  cases  of  dislocation  and  anchy- 
losis for  the  proofs  of  a  law  which  regulates  the  form  of  the 
muscular  system  in  its  normal  state.  Tt  would  be  easy  to 
show  that  these  scruples  have  no  foundation  ;  but  it  will  be 
better  still  to  bring  forward  other  examples  which  may  not  lie 
open  to  the  objections  so  often  urged  against  the  applications 
of  medicine  to  physiology. 

It  is  again  from  J.  Guerin,  that  we  must  quote  the  facts 
of  which  we  are  about  to  speak. 

When  we  examine  the  muscular  system  at  different  periods 
of  life,  we  find  that  it  varies  greatly  in  its  aspects.  It  seems 
that  the  muscles  have  distinct  ages,  and  that,  formed  at  first  of 
contractile  substance,  they  lose  by  degrees,  as  they  grow 
older,  their  red  fibres,  which  are  replaced  by  the  white  and 
glistening  fibres  of  the  tendon. 

Thus,  the  diaphragm  of  a  child  is  principally  muscular, 
while  in  the  old  man  the  aponeurotic  centre,  the  true  tendon 
of  the  diaphragm,  is  extended  at  the  expense  of  the  contrac- 
tile fibre.  The  substitution  of  tendon  for  muscular  fibre  is 
still  more  marked  in  the  muscles  of  the  leg  in  infancy ;  they 
are  relatively  much  more  rich  in  contractile  substance  than 
during  adult  age.  In  the  old  man,  in  fact,  the  tendon  seems 
to  invade  the  muscle,  so  that  the  portion  of  the  calf  of  the  leg 
which  remains  is  placed  very  high,  and  is  very  reduced  in 
length.  The  muscles  of  the  lumbar  and  dorsal  regions  present 
the  same  character ;  in  old  age  they  are  poorer  in  red  fibre, 
but  richer  in  tendon. 

What  theu,  is  the  change  which  takes  place  in  the  muscular 
function  during  the  diffeient  periods  of  life  ?  Every  one  knows 
that,  except  in  the  very  rare  cases  in  which  the  man  keeps  up 
the  habit  of  gymnastic  exercises,  the  muscular  function  be- 
comes mere  and  more  restricted — at  least,  as  far  as  the  extent 


VARIABILITY  OF  THE  MUSCULAR  SYSTEM.  99 


of  movement  is  concerned.  The  articulations  of  the  limbs,  and 
those  of  the  vertebral  column,  undergo  normally  a  sort  of 
incomplete  anchylosis,  which  continues  to  lessen  more  and 
more  the  flexibility  of  the  trunk. 

Look  at  a  young  child  tossing  about  at  his  ease :  one  of  his 
movements  is  to  play  with  his  foot ;  to  take  it  in  his  hands 
and  carry  it  to  his  mouth  appears  to  him  very  natural,  and  as 
easy  as  possible.  In  the  adult,  the  muscular  force  attains  its 
maximum ;  but  the  movements  are  not  so  extensive  as  in 
infancy ;  man  has  no  longer,  as  is  well  known,  the  same 
flexibility  in  his  limbs. 

The  old  man  can  neither  stoop  readily  nor  completely 
draw  himself  up  ;  his  vertebral  column  has  lost  its  supple- 
ness ;  he  takes  only  short  steps ;  to  sit  down  on  the  ground, 
with  the  knees  raised,  is  to  him  extremely  difficult ;  and  if 
we  examine  the  extent  of  flexion  and  extension  in  his  foot, 
we  find  that  it  has  become  very  limited. 

The  function  of  the  muscles,  therefore,  changes  with  the 
different  periods  of  life,  and  becoming  more  and  more  restricted, 
employs  continually  less  contractile  fibre.  It  is  thus  that  the 
muscular  modification  of  which  we  have  been  speaking  is 
naturally  explicable.  This  modification,  which  consists  in  the 
increase  of  the  tendinous  element  at  the  expense  of  red  fibre, 
may  be  prevented  by  keeping  up  the  extent  of  muscular 
movements,  by  means  of  suitable  exercise. 

Let  us  now  return  to  comparative  anatomy.  Since)  IF 
shows  us  perfect  harmony  between  the  form  of  the  muscles  in 
different  species  of  animals  and  the  characters  of  muscular 
function  in  the  same  species,  the  most  natural  conclusion  seems 
to  be  that  the  organ  has  been  subjected  to  the  influence  of 
function. 

If  the  race-horse  is  modified  in  its  form  by  the  special  exer- 
cise which  is  called  training,  is  it  not  an  evident  proof  of  the 
influence  of  function  on  the  anatomical  characters  of  the 
organism  ?  And  if  a  species,  thus  modified  artificially, 
returns  to  the  primitive  type  when  replaced  under  the  con- 
ditions from  which  it  had  been  taken,  is  it  not  the  counter- 
proof  of  the  theory  which  assigns  to  function  the  office  of 
a  modifier  of  the  organ  ? 


100 


ANIMAL  MECHANISM. 


These  very  facts  are,  however,  interpreted  in  an  opposite 
sense  by  the  partisans  of  the  invariability  of  species ;  they 
seem  to  find  an  unanswerable  argument  in  support  of  their 
cause,  in  the  return  to  the  primitive  type,  when  the  modifying 
influences  have  ceased. 

To  what  conclusion  can  we  come  when  we  meet  with  these 
contrary  opinions  ?    It  must  be  that  the  partisans  of  develop- 
ment have  not  completed  their  task,  and  that  they  ought  to 
add  new  proofs  to  those  which  they  have  already  given.  It 
is  to  experiment  that  the  principal  part  belongs,  while  theory 
is  not  without  its  importance ;  by  causing  us  to  foresee  in  what 
manner  a  certain  kind  of  function  ought  to  modify  a  muscle, 
.  it  will  give  its  proper  value  to  the  modification  which  may 
^^subsequently  be  obtained.    Indeed,  without  theory,  the  ex- 
Y~   perimenter  can  seldom  recognize  the  modification  which  he 
^__has  observed:     We  seldom  find  in  anatomy  anything  but 
that  which  we  seek  for,  especially  when  we  have  to  do  with 
slight  variations  like  those  which  we  might  hope  to  produce 
in  the  organism  of  an  animal. 

The  experiments  to  be  tried  are  tedious  and  troublesome ; 
their  plan,  however,  is  easy  to  trace. 

If  man,  adapting  to  his  necessities  the  domestic  animals, 
has  already  succeeded  in  modifying  their  organization  within 
certain  limits,  he  has  produced  these  changes,  as  we  may 
say,  fortuitously.  Only  intending,  for  example,  to  obtain 
draught  horses  or  racers,  it  was  not  necessary  to  place 
the  species  under  conditions  entirely  artificial.  This  must, 
however,  be  done,  if  we  aim  at  elucidating  the  problem  of 
which  we  speak,  and  of  carrying  to  the  farthest  possible 
limit,  changes  in  the  conditions  of  the  mechanical  work  of 
animals. 

Man  has  utilized  the  aptitudes  of  different  animals,  rather 
than  sought  to  give  them  new  ones.  It  would  be  necessary 
to  do  violence  to  the  habits  of  animals,  and  to  constrain 
them  gradually  to  perform  acts  to  which  their  organism  is 
but  slightly  adapted.  If,  in  order  to  get  its  food,  a  species 
with  an  organization  unsuitable  for  leaping,  should  be  com- 
pelled to  take  leaps  of  gradually  greater  height,  everything 
leads  us  to  suppose  that  it  would  acquire  at  length  great 


VARIABILITY  OF  THE  MUSCULAR  SYSTEM.  101 


facilities  for  leaping.  If  the  descendants  of  these  animals 
retained  any  of  the  power  of  their  ancestors,  they  might  per- 
haps, in  their  turn,  develop  still  more  this  faculty  of  leaping. 
Graduating  thus  the  effort  imposed  on  this  particular  species, 
no  longer  in  a  utilitarian  point  of  view,  which  there  would 
be  no  inducement  to  surpass,  but  requiring  indefinitely  more 
force  or  greater  extent  in  the  play  of  the  muscles,  we  might 
hope  that  the  anatomical  development  would  increase  indefi- 
nitely, and  that  we  might  obtain  something  analogous  to  that 
which  is  now  called  the  passage  of  one  species  into  another. 

What  we  have  said  of  the  muscular  function  applies  to  all 
the  rest.  By  modifying  in  a  gradual  manner  the  conditions 
of  the  food  of  animals,  as  well  as  those  of  light  and  dark- 
ness, temperature,  and  atmospheric  pressure  under  which  they 
may  be  made  to  live,  we  may  impress  upon  their  organism 
modifications  analogous  to  those  which  zoologists  have  already 
observed  under  the  influence  of  climate,  and  of  the  various 
atmospheric  conditions  and  different  altitudes  in  which  animals 
have  been  placed  by  nature.  These  changes,  brought  about 
by  well-managed  transitions  always  tending  to  the  same  end, 
would  have  a  chance  of  producing  considerable  transformations 
in  animal  organization,  provided  that,  by  persevering  determi- 
nation, these  efforts  were  indefinitely  accumulated ;  as  in  the 
case  of  breeders  of  animals,  who  use  similar  means  for  the 
production  of  selected  kinds  of  stock. 

We  will  proceed  no  farther  in  the  field  of  hypothesis,  but 
we  will,  in  conclusion,  make  an  appeal  to  zealous  experimen- 
talists. Many  who  have  been  convinced  of  the  great  import- 
ance of  this  enquiry  seem  already  to  be  engaged  in  this 
enterprise.  What  question,  in  fact,  can  more  nearly  coin  tin 
the  human  race  than  this:  Can  our  species  be  modified t 
According  to  the  tendency  which  may  be  given  to  it,  can  it  be 
directed  either  towards  perfection,  or  degradation  ? 

11 


4 


BOOK  THE  SECOND. 

FUNCTIONS:  TERRESTRIAL  LOCOMOTION. 


CHAPTER  I. 
OF  LOCOMOTION  IN  GENERAL. 

Conditions  common  to  all  kinds  of  locomotion— Borelli's  comparison— 
Hypothesis  of  the  reaction  of  the  ground — Classification  of  the  modes 
of  locomotion,  according  to  the  nature  of  the  point  of  resistance,  in 
terrestrial,  aquatic,  and  aerial  locomotion — Of  the  partition  of  muscular 
force  between  the  point  of  resistance  and  the  mass  of  the  body — Pro- 
duction of  useless  work  when  the  point  of  resistance  is  movable. 

The  most  striking  manifestation  of  movement  in  the  dif- 
ferent species  of  animals  is  assuredly  locomotion  :  the  act  by 
which  each  living  creature,  according  to  its  adaptation  to  out- 
ward circumstances,  moves  on  the  earth,  in  the  water,  or 
through  the  air.  Therefore  it  i3  more  convenient  to  study 
movement  with  regard  to  locomotion,  for  we  can  thus  observe 
it  under  the  most  varied  types. 

At  the  commencement  of  these  studies  we  ought  to  consider 
the  general  characteristics  of  the  function  which  is  to  occupy 
attention,  and  to  point  out  the  general  laws  which  are  to  be 
found  in  all  the  modes  of  animal  locomotion.  But  what  can 
be  more  difficult  than  to  ascertain  the  common  features  which 
unite  acts  so  different  as  those  of  flying  and  of  creeping,  as 
the  gallop  of  a  horse  and  the  swimming  of  a  fish  ?  Still  this 
has  been  frequently  attempted.  Borelli  has  endeavoured  to 
represent  the  various  modes  of  terrestrial  locomotion,  by  the 
different  methods  which  a  boatman  employs  to  direct  his  boat. 

This  comparison  may,  with  some  additional  developments, 
serve  to  explain  the  mechanism  of  the  principal  types  of  loco- 
motion. 


LOCOMOTION  IN  GENERAL. 


103 


Let  us  suppose  a  man  seated  in  a  boat  in  the  midst  of  a 
tranquil  lake.  Under  these  conditions,  his  skiff  will  remain 
perfectly  motionless.  If  he  wishes  to  advance,  he  must  find 
what  is  called  a  point  of  resistance.  Suppose  him  to  be  fur- 
nished with  a  pole,  he  will  plunge  it  towards  the  bottom  of 
the  water  till  it  reaches  the  ground ;  then,  making  an  effort, 
as  if  to  drive  from  him  thi3  resisting  body,  he  will  cause  his 
boat  to  move  in  the  opposite  direction.  This  progression  with 
the  point  of  resistance  on  the  ground  is  similar  to  the  ordinary 
conditions  of  terrestrial  locomotion. 

If  the  boatman  be  provided  with  a  boat-hook,  he  will 
get  his  point  of  resistance  under  different  conditions.  Laying 
hold  of  the  branches  of  trees,  or  the  projections  of  the  shore, 
he  will  drag  his  pole  towards  himself,  as  if  to  bring  near  to 
him  the  bodies  to  which  it  is  fastened ;  and  if  these  bodies 
resist  his  efforts,  the  boat  alone  will  be  displaced  and  drawn 
towards  them. 

Here  are  then  two  opposite  modes  of  progression  with 
bearings  on  solid  bodies ;  in  one  the  tendency  is  to  repel,  in  the 
other,  to  draw  them  nearer :  the  effect  is  the  same  in  each  case. 

But  if  the  lake  be  too  deep,  or  if  the  shores  be  too  distant 
to  furnish  the  boatman  with  the  solid  fulcrum  which  he  had 
used  before,  the  water  itself  will  serve  as  a  medium  of 
resistance.  The  boatman,  armed  with  a  flattened  oar,  endea- 
vours to  drive  the  water  towards  the  stern  of  his  boat ;  the 
water  will  yield  to  this  impulse,  but  the  boat,  impelled  in 
an  opposite  direction,  will  go  forward.  The  various  kinds  of 
paddles  for  steam-boats,  the  screw,  in  fact,  all  nautical  pro- 
pellers, present  this  feature  in  common,  of  driving  the  water 
backward,  in  order  to  produce  in  the  boat  an  impulse  in  the 
contrary  direction,  and  to  cause  it  to  advance. 

Instead  of  an  oar  acting  on  the  water,  we  may  suppose  the 
boatman  provided  with  a  much  larger  paddle  with  which  he 
might  drive  back  the  air  at  the  stern  ;  he  will  propel  his 
boat  on  the  surface  of  the  lake.  He  might  make  progress 
also  by  turning  a  large  screw  like  the  sails  of  a  wind- 
mill, or  by  agitating  at  the  stern  some  large  fan  which  would 
drive  the  air  in  the  direction  opposed  to  that  in  which  he 
desired  to  force  his  boat. 


ANIMAL  MECHANISM, 


la  all  these  modes  of  locomotion  a  force  is  expended  which 
impels  in  opposite  directions  two  bodies  more  or  less  resisting ; 
the  one  is  the  fulcrnm,  the  other  the  weight  to  be  displaced. 

Old  writers  called  the  force  acting  on  the  boat  re-  action — 
they  considered  it  as  an  effort  emanating  from  the  soil,  the 
water,  or  any  resistance  whatever  to  which  the  effort  of  the 
rowers  was  applied.  We  can  now  understand  clearly  that  all 
the  motive  force  is  derived  from  the  boatman.  This  force  can 
have  as  its  result,  either  the  repulsion  of  two  points  to  which 
it  is  applied,  or  their  approach  to  each  other.  In  these  two 
cases  one  of  the  points  may  be  fixed,  it  is  then  the  other  which 
will  be  displaced ;  or  the  two  points  may  be  movable,  and 
then,  according  to  their  unequal  movability,  one  of  them  will 
be  displaced  more  than  the  other. 

This  general  principle  can  be  applied  to  all  cases  of  loco- 
motion ;  it  will  be  sufficient  for  us  to  notice  that  which  is 
essential  in  all  the  types  which  we  shall  consider. 

The  most  natural  classification  seems  to  be  that  which  is 
based  on  the  nature  of  the  point  of  resistance  ;  accordingly,  we 
may  distinguish  three  principal  forms  of  locomotion — terres- 
trial, aquatic,  or  aerial.  But  in  each  of  these  forms,  w7hat  a 
variety  of  mechanism  we  shall  meet  with  ! 

If  it  be  true  that  walking  and  creeping  are  the  two 
principal  types  of  terrestrial  motion,  that  swimming  corre- 
sponds with  the  more  habitual  mode  of  aquatic  locomotion, 
and  flight  with  aerial  locomotion,  it  is  not  less  true  that  in 
certain  media  many  kinds  of  locomotion  are  employed.  Thus, 
walking  and  creeping  are  used  both  on  the  earth  and  in  the 
water ;  flight  is  habitually  performed  in  the  air,  and  yet 
certain  birds  take  a  decided  flight  in  the  water. 

In  fact,  if  we  were  compelled  to  assign  to  every  animal  its 
particular  type  of  locomotion,  our  embarrassment  would  be 
as  great  as  if  we  were  classifying  these  movements.  Some, 
indeed,  move  with  an  equal  facility  on  the  earth,  the  water, 
and  in  the  air.  We  will  not  therefore  attempt  a  strictly 
methodical  classification  of  the  different  modes  of  locomotion 
of  which  we  are  about  to  take  a  rapid  survey. 

Terrestrial  locomotion  furnishes  two  principal  types  :  in  one 
the  effort  consists  in  pressing  on  the  ground  in  the  direction 


LOCOMOTION  IN  GENERAL. 


105 


opposite  to  the  intended  movement;  this  is  the  more  usual  mode 
of  locomotiou ;  walking,  running,  leaping,  belong  to  this  first 
form.  For  this  purpose  the  limbs  serving  for  locomotion  are 
composed  of  a  series  of  rigid  levers,  susceptible  of  change  in 
length ;  they  can  be  shortened  by  the  angular  flexion  of  the 
articulations,  and  they  grow  longer  by  being  drawn  up.  If 
the  leg  when  bent  touches  the  ground  at  its  extremity,  and  if 
a  muscular  effort  be  made  to  produce  the  extension  of  the 
limb,  this  can  only  be  effected  by  removing  to  a  greater  dis- 
tance from  each  other  the  ground  on  which  the  extremity  of 
the  leg  rests  and  the  body  of  the  animal  which  is  united 
to  the  base  of  this  limb  ;  the  ground  offers  resistance,  and  the 
body,  yielding  to  the  impulse,  is  displaced.  Sometimes  the 
displacement  in  terrestrial  locomotion  is  effected,  not  by  a 
change  in  length,  but  by  a  simple  change  of  the  angle  formed 
between  the  limb  which  causes  the  motion  and  the  body  of 
the  animal. 

In  the  second  type,  namely  creeping,  a  tractile  effort  is  pro- 
duced ;  the  animal  lays  hold  by  a  part  of  its  body  on  an  ex- 
ternal fixed  point,  and  then  drags  the  mass  of  its  bulk  towards 
this  point.  Let  us  take  a  snail,  and  place  it  on  a  piece  of 
transparent  glass ;  at  the  end  of  a  few  moments  the  animal 
begins  to  crawl.  If  we  turn  the  glass  over,  we  shall  see 
through  the  plate  the  details  of  its  movements.  Throughout 
all  the  length  of  its  body  appears  a  series  of  transverse  bands, 
alternately  pale  and  deeply  coloured,  opaque  and  transparent. 
These  bands  are  transmitted  by  a  continual  motion,  from  the 
tail  to  the  head  of  the  animal ;  they  seem  like  the  spirals  of 
a  screw  which  turns  incessantly  in  the  same  direction.  If  we 
fix  our  attention  on  one  of  these  bands  in  the  neighbourhood 
of  the  tail,  we  see  it  pass  towards  the  head,  which  it 
reaches  in  fifteen  or  twenty  seconds,  but  it  is  followed  by 
a  continued  series  of  bands  which  seem  to  spring  up  behind 
it  as  it  advances.  These  bands  remind  us  of  the  muscu- 
lar wave  and  its  progress  through  a  contracting  fibre,  only 
with  greater  dimensions.  Each  time  that  a  wave  arrives 
at  the  cephalic  region  of  the  animal,  it  disappears,  producing  a 
forward  motion  of  the  head,  which  slips  a  little  on  the  surface 
of  the  glass  and  advances  slightly  without  any  retrogression. 


106 


ANIMAL  MECHANISM. 


It  appears  that  the  cephalic  region  lays  hold  on  the  fixed 
point  towards  which  all  the  rest  of  the  body  is  dragged  for- 
ward. In  fact,  in  the  posterior  region  an  opposite  phenome- 
non takes  place  ;  each  new  band  which  takes  its  rise  there,  is 
accompanied  by  a  backward  motion  of  that  region,  which  moves 
as  if  it  were  drawn  by  a  longitudinal  retraction  of  the  con« 
tractile  tissue. 

Other  modes  of  creeping  are  not  less  curious ;  that,  for 
example,  which  takes  place  in  the  interior  of  a  solid  body  ; 
as  a  worm,  when  it  advances  in  the  tubular  cavity  which  it 
has  hollowed  out  in  the  ground.  The  hinder  part  of  the  body, 
soft  and  extensible,  is  assuredly  of  much  less  size  than  the 
cavity  of  the  hole  from  which  we  endeavour  to  pull  it,  and 
yet  the  worm  resists  the  force  of  traction,  and  breaks  rather 
than  be  drawn  out.  This  is  because,  within  the  ground, 
the  anterior  portion  of  the  body,  shortened  but  swollen,  dilates 
within  the  passage,  and  finds  there  a  solid  point  of  resistance. 
If  we  let  the  worm  go  we  shall  see  it  rapidly  shorten  its 
body,  and  withdraw  the  rest  of  it  into  the  ground,  being 
dragged  backward  towards  the  anterior  portion  which  has  a 
firm  hold  on  the  soil. 

By  the  side  of  the  action  of  creeping  we  may  naturally 
place  that  of  climbing,  in  which  the  anterior  limbs  seek  to  lay 
hold  of  some  elevated  projection,  and  as  they  bend  raise  the 
rest  of  the  body  of  the  animal.  The  hinder  part  then  fixes 
itself  in  its  new  position,  and  the  anterior  limbs,  thus  set  free, 
seek,  higher  up,  a  fresh  resting  place  to  make  a  new  effort. 
What  different  types  in  these  two  modes  of  terrestrial  locomo- 
tion !  The  varieties  are  so  great  that  we  can  scarcely  give 
an  exact  idea  of  them,  except  by  describing  the  mode  of  pro- 
gression adopted  by  each  particular  animal. 

Locomotion  in  water  presents  a  still  greater  diversity.  In 
one  case,  we  see  a  fish  which  strikes  the  water  with  the  flat 
of  its  tail ;  in  another,  a  cuttle  fish  or  a  medusa,  which,  com- 
pressing forcibly  its  pouch  full  of  liquid,  drives  out  the  water 
in  one  direction  and  propels  itself  in  a  course  directly  opposite  ; 
the  same  phenomenon  is  produced  when  a  mollusk  closes  rapidly 
the  valves  of  its  shell,  and  projects  itself  in  the  direction  opposed 
to  the  current  of  water  which  it  has  produced.    The  larvae  of 


LOCOMOTION  IN  GENERAL. 


107 


dragon-flies  expel  from  their  intestines  a  very  strong  jet  of  liquid, 
and  acquire,  by  this  means,  a  rapid  and  forcible  impulse. 

The  oar  is  found  in  many  insects  which  move  on  the  sur- 
face of  the  water.  A  contrivance  is  employed  by  other 
animals,  which  resembles  the  action  of  an  oar  used  at  the 
stern  of  a  boat  in  the  process  called  sculling.  To  this 
latter  motive  power  may  be  referred  all  those  movements 
in  which  an  inclined  plane  is  displaced  in  the  liquid, 
and  finds  in  the  resistance  of  the  water,  which  it  presses 
obliquely,  two  component  forces,  of  which  one  furnishes  a 
movement  of  propulsion.  This  mechanism  will  require  some 
explanation;  it  will  be  found  in  its  proper  place,  with  all 
the  developments  which  it  affords. 

Aerial  locomotion.  This  mechanism  is  still  the  same ;  the 
motion  of  an  inclined  plane,  which  causes  motion  through 
the  air.  The  wing,  in  fact,  in  the  insect  as  well  as  in 
the  bird,  strikes  the  air  in  an  oblique  manner,  repels  it  in  a 
certain  direction,  and  gives  the  body  a  motion  directly  oppo- 
site. With  the  exception  of  certain  birds  which  spread  their 
wings  to  the  wind,  and  which,  hovering  thus  without  any 
other  effort  than  simply  steering,  have  received  the  picturesque 
name  of  hovering  or  sailing  birds  (oiseaux  voiliers),  all 
animals  move  forward  only  by  an  effort  exerted  between  two 
masses  unequally  movable.  It  can  be  easily  understood  that 
if  one  of  these  points  where  the  force  is  applied  is  absolutely 
fixed,  the  other  alone  will  receive  without  diminution  the 
motive  work  developed  ;  such  is  the  condition  of  terrestrial 
locomotion  on  soil  perfectly  solid.  But  we  can  understand 
also  that  the  softness  of  the  ground  constitutes  a  condition  un- 
favourable to  the  utilization  of  the  force  employed,  and  that 
the  extreme  mobility  both  of  the  air  and  the  water  offer  still 
less  favourable  conditions  for  swimming  or  flight. 

But  this  mobility  of  the  point  of  resistance  varies  with  the 
rapidity  of  the  movement ;  so  that  a  certain  stroke  of  the 
wing  or  the  oar,  which  would  be  without  effect  if  produced 
6lowly,  would  become  efficacious  by  its  very  rapidity. 

In  different  kinds  of  locomotion,  the  resistance  which  it 
is  necessary  to  overcome  in  order  to  displace  the  body,  does 
not  vary  less  than  that  which  serves  as  an  external  point  of 


108 


ANIMAL  MECHANISM. 


resistance.  This  variability  depends  on  many  causes.  Thus, 
different  kinds  of  animals,  when  they  move,  have  not  to 
struggle  with  the  same  effort  against  their  weight.  The  fish, 
which  is  of  nearly  the  same  specific  gravity  as  water,  finds 
itself  suspended  in  it  without  having  to  exert  any  force; 
and  if  it  wishes  to  move  in  any  direction,  it  has  only  to 
overcome  the  resistance  of  the  fluid  which  it  is  necessary 
to  displace.  The  bird,  on  the  contrary,  if  it  desires  to  sus- 
tain itself  in  the  air,  must  make  an  effort  capable  of 
neutralizing  the  action  of  its  weight.  If  it  moves  forward 
at  the  same  time,  it  must  perform,  in  addition,  the  work 
which  is  consumed  in  overcoming  the  resistance  of  the  air. 

Partition  of  muscular  force  between  the  points  of  resistance  and 
the  mass  of  the  body.  When,  in  physiology,  we  seek  to  es- 
timate the  work  of  a  muscle,  we  fix  it  firmly  by  one  of  its 
attachments,  and  we  ascertain  the  extent  passed  through 
by  its  movable  extremity.  If  we  know  the  weight  which 
this  muscle  can  raise  as  it  contracts,  and  the  extent  through 
which  that  weight  is  raised,  we  have  elements  by  which  we 
can  estimate  the  work  effected.  But  these  are  almost  ideal 
conditions,  which  are  scarcely  ever  found  in  terrestrial  loco- 
motion ;  nor  can  we  observe  them  in  animals  which  move  in 
the  water,  and  more  especially  in  those  which  fly  through  the 
air.  Let  us  only  compare  the  effort  necessary  to  walk  on  a 
movable  soil,  on  sandy  dunes,  for  instance,  with  that  required 
in  walking  on  firm  soil.  We  shall  see  that  the  mobility  of 
the  resisting  surface  presented  by  the  sand  destroys  a  part  of 
the  effort  necessary  for  the  contraction  of  our  muscles;  in 
other  words,  that  a  greater  effort  is  necessary  to  produce  the 
same  useful  work,  when  the  point  of  resistance  is  not  stable. 

This  amount  of  work  is  easy  to  be  understood,  and  even  to 
be  measured. 

When  a  man,  while  walking,  places  one  of  his  feet  on  the 
ground,  the  corresponding  leg,  slightly  bent,  draws  itself  up, 
and  pressing  on  the  ground  below,  gives  at  the  same  time  an 
upward  impulse  to  the  body.  If  the  ground  entirely  resist 
this  pressure,  all  the  movement  produced  will  be  in  the 
direction  of  the  trunk  of  the  body,  which  will  be  raised 
to  a  certain  height,  three  centimetres  for  example.    But  if 


LOCOMOTION  IN  GENERAL. 


109 


the  ground  sink  two  centimetres  under  the  pressure  of  the 
foot,  it  is  evident  that  the  body  will  only  be  raised  one 
centimetre,  and  the  useful  work  will  be  diminished  by  two- 
thirds. 

The  compression  of  the  soil  under  the  foot  certainly  con- 
stitutes work,  according  to  the  mechanical  definition  of  this 
word.  In  fact,  the  soil,  as  it  yields,  offers  a  certain  resist- 
ance. This  resistance  must  be  multiplied  by  the  extent  to 
which  the  soil  is  indented,  in  order  to  ascertain  the  value  of 
the  work  accomplished  in  this  direction.  But  this  work  is 
absolutely  useless  with  respect  to  locomotion :  it  is  an  entire 
loss  of  the  motive  force  expended. 

When  a  fish  strikes  the  water  with  his  tail,  in  order  to 
drive  himself  forward,  he  executes  a  double  work  ;  a  part 
tends  to  drive  behind  him  a  certain  mass  of  fluid  with  a 
certain  velocity,  and  the  other  to  drive  the  animal  forward  in 
spite  of  the  resistance  of  the  surrounding  water.  This  last 
work  alone  is  utilized ;  it  would  be  much  more  considerable 
if  the  tail  of  the  animal  met  with  a  solid  point  of  resistance 
instead  of  the  water  which  flies  from  before  it. 

Is  it  possible  to  measure  the  diminution  of  useful  work 
in  locomotion,  according  to  the  greater  or  less  mobility  of  the 
point  of  resistance  ? 

If  the  ground  on  which  we  walk  resist  perfectly,  it  must  be 
admitted  that  no  part  of  the  muscular  work  is  lost;  but  in 
every  case  in  which  a  displacement  of  the  resisting  surface 
exists  at  the  same  time  as  that  of  the  body,  it  is  necessary  to 
determine  the  law  according  to  which  this  partition  is  made. 
A  principle  established  by  Newton  regulates  the  science  of 
mechanics ;  this  is  that  "  action  and  re-action  are  equal." 
Does  this  mean,  in  the  case  before  us,  that  half  of  the  work 
is  expended  on  the  resisting  surface,  and  the  other  half  on 
the  displacement  of  the  body  of  the  animal  ?  This  cannot  be 
true,  if  we  may  judge  by  the  many  cases  in  which  a  force  acts 
on  two  bodies  at  the  same  time. 

Thus,  in  the  science  of  projectiles,  the  motive  force  of  the 
powder — that  is  to  say,  the  pressure  of  the  gases  which  are 
disengaged  in  the  cannon,  acts  at  the  same  time  on  the  pro- 
jectile and  on  the  piece,  giving  these  masses  a  velocity  in 


110 


ANIMAL  MECHANISM. 


opposite  directions.  Thus,  the  momentum  (M.V.)  is  equally 
divided  between  the  two  projectiles,  so  that  the  mass  of  the 
cannon  and  of  its  carriage,  multiplied  by  the  velocity  of  the 
recoil  which  is  communicated  to  it,  is  equal  to  the  mass  of 
the  projectile  multiplied  by  the  velocity  of  propulsion  which 
it  receives.  As  the  cannon  weighs  much  more  than  the  ball, 
the  velocity  of  its  recoil  is  much  less  than  that  communi- 
cated to  the  projectile. 

As  to  the  work  developed  by  the  powder  against  the  cannon 
and  against  the  ball,  it  is  divided  very  unequally  between 
these  two  masses. 

In  fact,  the  work  produced  by  an  active  force  being  pro- 
portional to  the  square  of  the  velocity  of  the  mass  in  motion 
(its  formula  is  ^p)y  calculation  shows  that  this  work,  when 
the  piece  weighs  300  times  more  than  the  ball,  would  be  300 
times  greater  for  the  ball  than  for  the  cannon. 

We  shall  return  to  these  questions,  when  in  considering  the 
particular  kinds  of  animal  motion,  we  enter  on  the  investiga- 
tion of  human  locomotion. 


CHAPTER  II. 

TERRESTRIAL  LOCOMOTION  (BIPEDS). 

Choice  of  certain  types  in  order  to  study  terrestrial  locomotion— Human 
locomotion— Walking— Pressure  exerted  on  the  ground,  its  duration 
and  intensity — Re-actions  on  the  body  during  walking— Graphic 
method  of  studying  them — Vertical  oscillations  of  the  body — 
Horizontal  oscillations— Attempt  to  represent  the  trajectory  of  the 
pubis — Forward  movement  of  the  body— Inequalities  of  its  velocity 
during  the  time  occupied  by  a  pace. 

ACT   OF   WALKING   IN  MAN. 

The  types  of  terrestrial  locomotion  are  so  various  that  we 
must,  for  a  time  at  least,  confine  ourselves  to  the  study  of  the 
most  important  among  them.  For  locomotion  among  bipeds 
we  will  take  as  a  type  that  of  man.   The  horse  will  be  chosen 


TERRESTRIAL  MOTION  (man). 


Ill 


as  the  most  important  representative  of  the  method  of  walking 
adopted  by  quadrupeds.  As  to  other  animals,  they  will  be 
studied  in  an  accessory  manner,  and  especially  with  reference 
to  the  resemblances  and  differences  which  the  modes  of  their 
locomotion  present  when  compared  with  the  types  which  we 
have  chosen. 

Many  authors  have  already  treated  on  this  subject;  from 
the  time  of  Borelli  to  that  of  modern  physiologists,  science 
has  slowly  advanced :  it  seems  to  us  that  it  can  now  resolve 
all  obscure  questions,  and  determine  them  definitely,  by  the 
employment  of  the  graphic  method. 

While  observation  employed  alone  furnishes  only  incom- 
plete and  sometimes  false  data,  the  graphic  method  carries  its 
precision  into  the  analysis  of  the  very  complex  movements 
concerned  in  locomotion.  We  shall  see,  when  we  treat  of  the 
paces  of  the  horse,  that  the  disagreement  we  find  among 
writers  on  this  subject  shows  clearly  the  insufficiency  of  the 
methods  hitherto  employed. 

Human  locomotion,  though  much  more  simple  in  its  mechan- 
ism, is  still  very  difficult  to  analyse ;  the  works  of  the  two 
Webers,  though  considered  as  the  deepest  investigation  of 
human  locomotion  that  have  yet  been  made,  show  many 
omissions  and  some  errors. 

The  most  simple  and  usual  pace  is  walking,  which,  according 
to  the  received  definition,  consists  in  that  mode  of  locomotion 
in  which  the  body  never  quits  the  ground.  In  running  and 
leaping,  on  the  contrary,  we  shall  see  that  the  body  is  en- 
tirely raised  above  the  ground,  and  remains  subpended  during 
a  certain  time. 

In  walking,  the  weight  of  the  body  passes  alternately  from 
one  leg  to  the  other,  and  as  each  of  these  limbs  places  itself 
in  turn  before  the  other,  the  body  is  thus  continually  carried 
forward.  This  action  appears  very  simple  at  first  sight,  but 
its  complexity  is  soon  observed  when  we  seek  to  ascertain 
what  are  the  movements  which  concur  in  producing  this 
motion. 

We  see,  in  fact,  that  each  movement  of  the  limbs  brings 
under  consideration  a  phase  of  impact  and  one  of  support  in 
each  of  these ;  the  different  articulations  bend  and  extend 


112 


ANIMAL  MECHANISM. 


alternately,  while  tlie  muscles  of  the  leg  and  the  thigh,  which 
produce  these  movements,  pass  through  alternations  of  con- 
traction and  relaxation. 

The  intensity  of  the  pressure  of  the  feet  on  the  ground 
varies  with  the  rapidity  of  walking  and  with  the  length  of  the 
step.  Besides  this,  the  body  passes  through  periodical  oscil- 
lations, the  re-action  of  the  impact  of  each  foot  on  the  ground; 
and  the  different  parts  of  the  body  are  subject  to  this  re-action 
in  various  degrees.  These  oscillations  are  produced  in  diffe- 
rent directions;  some  are  vertical,  others  horizontal,  so  that 
the  trajectory  which  follows  any  point  of  a  body  is  a  very 
complex  curve.  In  addition  to  this,  the  body  is  inclined  and 
drawn  up  again  at  each  movement  of  one  of  the  legs ;  it 
revolves  as  on  a  pivot  round  the  coxo-femoral  articulation,  at  the 
same  time  that  it  is  slightly  bent  following  the  axis  of  the 
vertebral  column;  and,  under  the  action  of  the  lumbar  muscles, 
the  pelvis  moves  and  oscillates  with  a  sort  of  rolling  motion. 
At  the  same  time  the  anterior  limbs,  exerting  an  alternate 
balancing  power,  lessen  the  influences  which,  at  each  instant, 
tend  to  cause  the  body  to  deviate  from  the  straight  course 
which  it  strives  to  maintain. 

All  these  acts  have  been  analysed  with  much  sagacity  by 
one  of  our  pupils,  Mons.  G.  Carlet,*  from  whom  we  quote  some 
of  the  results  which  he  has  obtained. 

The  motive  force  developed  in  walking,  its  pressure  on  the 
ground  in  one  direction,  and  its  propelling  effects  on  the  mass 
of  the  body  on  the  other  hand,  are  the  three  elements  which 
will  at  first  occupy  our  attention. 

Motive  force.  This  is  found  in  the  action  of  the  exterior 
muscles  of  the  thigh,  the  leg,  and  the  foot.  The  lower  limb 
forms,  as  a  whole,  a  broken  column,  whose  angles  are  rounded 
off,  and  whose  return  to  the  perpendicular  is  effected  by  pres- 
sure on  the  ground  below,  and  on  the  body  above.  This  is  all 
that  we  can  say  on  this  head,  which,  if  treated  more  at  length, 
would  require  considerable  amplifications. 

Pressure  on  the  ground.  This  pressure,  equal,  as  we  have 
before  seen,  to  that  in  the  opposite  direction,  which  tends  to 
impel  the  body  forward,  must  be  studied  in  its  duration,  its 
*  G.  Carlet,  £tude  de  la  Marche.  Annales  des  Sciences  naturelles,  1872. 


WALKING. 


113 


phases,  and  its  intensity.  The  registering  apparatus  enables  us 
to  do  this  perfectly  ;  an  experimental  instrument  placed  under 
the  sole  of  the  foot  is  connected  with  a  lever  which  gives  the 
signals  of  the  impact  and  of  the  rising  of  the  foot,  as  well  as 
the  expression  of  the  force  with  which  the  foot  is  pressed  upon 
the  ground.  We  call  this  first  instrument  the  experimental 
shoe,  which  may  be  thus  described : — 

Under  the  sole  of  an  ordinary  shoe  is  fixed  with  heated 
gutta  percha  a  strong  sole  of  india-rubber  1  J  centimetres  in 
thickness.  Within  this  sole  there  is  an  air  chamber,  which 
in  fig.  1 9  is  represented  by  dotted  lines. 


Fio.  19.— Experimental  shoe,  intended  to  show  the  pressure  of  the  foot 
on  the  ground,  with  its  duration  and  its  phases. 

This  chamber,  having  upon  it  a  small  piece  of  projecting 
wood,  is  compressed  at  the  moment  that  the  foot  exerts  its 
pressure  on  the  ground.  The  air  expelled  from  this  cavity 
escapes  by  a  tube  into  a  drum,  with  a  lever  attached,  which 
registers  the  duration  and  the  phases  of  the  pressure  of 
the  foot. 

Let  us  suppose  that  the  experimenter  is  provided  on  both 
feet  with  similar  shoes,  and  that  he  walks  at  a  regular  pace 
round  a  table  which  supports  the  registering  apparatus ;  we 
shall  then  understand  the  arrangement  of  the  experiment. 

The  registering  instruments  employed  are  already  known  to 
the  reader;  they  resemble  in  all  points  those  which  have 
12 


114 


ANIMAL  MECHANISM. 


served  for  the  investigation  of  the  muscular  wave  (fig.  7, 
page  37).  If  we  substitute  in  this  figure  an  experimental 
shoe  for  each  of  the  myographical  clips  1  and  2,  we  shall 
have  the  arrangement  of  the  apparatus  necessary  for  the  study 
of  footsteps  or  impacts  of  the  foot  on  the  ground. 

Fig.  20  has  been  furnished  by  an  experiment  in  walking. 
Two  tracings  are  given  by  the  intermittent  pressure  of  the 
feet  on  the  ground.  The  full  line  D  corresponds  with  the 
right  foot ;  the  dotted  line  with  the  left. 


Fig.  20. — Tracings  of  the  impact  and  the  rise  of  the  two  feet  in  our  ordinary  walk. 


Knowing  the  arrangement  of  the  apparatus,  we  can  under- 
stand that  each  impact  of  the  foot  on  the  ground  will  be 
represented  by  the  elevated  part  of  the  corresponding  curve. 
In  fact,  the  pressure  of  the  foot  on  the  ground  compresses  the 
india-rubber  sole  and  diminishes  the  capacity  of  the  included 
air-chamber.  A  part  of  the  contained  air  escapes  by  the  con- 
necting tube,  and  passes  into  the  registering  drum. 

We  see  in  fig.  20  that  the  pressure  of  the  right  foot,  for 
instance,  commences  at  the  moment  when  that  of  the  left 
begins  to  decrease  ;  and  that  in  all  the  tracings  there  is  an 
alternation  between  the  impacts  of  the  two  feet.  The  period 
of  support  of  each  foot  is  shown  by  a  horizontal  line  which 
joins  the  minima  of  two  successive  curves. 

The  impacts  of  the  right  and  left  feet  have  the  same  dura- 
tion, so  that  the  weight  of  the  body  passes  alternately  from 
one  foot  to  the  other.  It  would  not  be  the  same  with  respect 
to  a  lame  person  ;  lameness  corresponds  essentially  with  the 
inequality  of  the  impacts  of  the  two  feet. 

There  is  always  a  very  short  period  during  which  the  body 
is  partially  supported  by  one  foot,  but  when  it  already  be- 
gins to  rest  on  the  other ;  this  time  is  scarcely  equal  to  the 


WALKING. 


115 


6i*xth  part  cf  the  duration  of  a  single  impact  or  pressure  of 
the  foot. 

Intensity  of  the  pressure  of  the  foot  upon  the  ground.  —  The 
curves  traced  by  walking  may  also  furnish  the  measure  of  the 
effort  exerted  by  the  foot  upon  the  ground.  The  experimental 
shoes  constitute  a  kind  of  dynameter  of  pressure ;  they  com- 
press the  drum,  less  or  more,  according  to  the  effort  they 
exert ;  and  consequently  they  transmit  to  the  registering  lever 
more  or  less  extensive  movements.  In  order  to  estimate, 
according  to  the  elevation  of  the  curve,  the  pressure  exerted 
by  the  foot,  we  must  substitute  for  the  weight  of  the  body  a 
certain  number  of  kilogrammes.  We  see  thus  that,  if  the 
weight  of  the  body  (75  kilogrammes,  for  example)  is  sufficient 
to  raise  the  lever  to  the  height  which  it  attains  at  the  com- 
mencement of  each  curve,  an  additional  weight  will  be  required 
to  raise  it  to  the  maximum  elevation  which  it  attains  towards 
the  end  of  its  period  of  pressure. 

That  proves  that,  in  walking,  the  pressure  of  the  foot  on 
the  ground  is  not  only  equal  to  the  weight  of  the  body  which 
the  foot  has  to  sustain,  but  that  a  greater  effort  is  produced  at 
a  given  moment  in  order  to  give  the  body  the  movements  of 
elevation  and  progression  which  we  have  just  been  studying. 

According  to  Mons.  Carlet,  this  additional  effort  is  not  more 
than  20  kilogrammes,  even  in  rapid  walking,  but  it  is  much 
greater  in  running  and  leaping. 

Reactions. — We  shall  designute  by  this  name  the  movements 
which  the  action  of  the  leg  produces  on  the  mass  of  the  body. 
These  movements  are  very  complex;  they  are  effected  at  the 
same  time  in  every  direction,  and  give  to  the  trajectory 
which  a  point  of  the  body  describes  in  space,  some  very  com- 
plicated sinuosities.  The  graphic  method  alone  can  enable 
ns,  at  least  as  yet,  to  appreciate  the  real  nature  of  these 
movements. 

In  the  first  place,  what  point  of  the  body  6hall  we  choose 
in  order  to  observe  the  displacement  caused  by  the  act  of 
walking?  Almost  all  authors  have  taken  for  this  purpose  the 
centre  of  gravity,  the  point  which  Borelli  places  inter  nates  et 
pubim.  But  if  we  reflect  that  the  centre  of  gravity  changes 
as  soon  as  the  body  moves,  that  in  the  flexion  of  the  legs  this 


116 


ANIMAL  MECHANISM. 


centre  rises,  that  it  is  altered  if  we  raise  our  arms,  that,  in 
fact,  it  describes  within  the  interior  of  the  body  all  sorts  of 
movements,  as  soon  as  we  cease  to  be  motionless,  it  is  easy 
to  understand  that  it  will  be  impossible  to  refer  to  this 
ideal  and  movable  point,  the  reactionary  movements  produced 
by  the  pressure  of  the  feet  upon  the  ground.  It  will  be 
better  to  choose  a  determinate  part  of  the  trunk  of  the  body, 
the  pubis,  for  example,  in  order  to  study  its  movements  in  the 
act  of  walking. 


Fig.  21. — Transmission  of  an  oscillatory  movement  to  the  registering  apparatus. 


The  instrument  which  we  have  already  employed  will  be 
applicable  to  the  study  of  these  displacements. 

Let  there  be  two  lever  drums,  united  by  a  long  tube  T  T  T. 
Let  a  vertical  oscillary  movement  be  given  to  one  of  these 
levers,  so  as,  for  example,  to  carry  the  lever  L  downwards 
into  the  position  indicated  by  the  dotted  line,  the  other  lever 
will  be  displaced  in  the  opposite  direction,  and  will  assume  the 
position  also  shown  by  the  dotted  line  near  it.  Under  these 
conditions  the  lowering  of  one  lever  corresponds  with  the  ele- 
vation of  the  other,  since  the  compression  of  the  air  in  one  of 
the  drums  must  lead  to  its  expansion  in  the  other.  If  we 
wish  to  obtain  from  the  two  parts  of  the  apparatus  indications 
in  the  same  direction,  it  would  be  necessary  to  turn  one  of 
the  drums,  so  as  to  place  its  lever  downwards. 

Vertical  oscillations  of  the  body. — Let  us  suppose  that  one  of 
these  levers  traces  a  curve  on  the  registering  apparatus,  while 
the  o!her  rests,  by  its  point,  on  the  pubis  of  a  man  who  is 


WALKING. 


117 


walking ;  all  the  vertical  oscillations  of  the  pubis  will  be 
registered. 

But,  in  order  that  the  experimental  lever  may  receive  and 
transmit  faithfully  the  vertical  oscillations  which  the  pubis 
executes  during  the  act  of  walking,  the  drum  itself  must  be 
protected  from  these  oscillations.  For  this  purpose  an  instru- 
ment has  been  invented,  composed  of  two  horizontal  arms, 
which  turn  on  a  centre.  These  arms  can  move  only  in  a  hori- 
zontal plane,  situated  at  the  height  of  the  pubis  of  the  person 
under  experiment ;  to  one  of  these  arms  is  fixed  the  experi- 
mental lever  drum. 


jf  ~x_  _x~ 

1 

FlG.  22. — The  upper  curves,  one  in  full  line,  the  other  do»ted.  represent 
the  phases  of  the  impact  and  of  the  rise  of  the  light  and  left  loot.  Reading 
the  figure  from  left  to  right,  each  rise  of  the  curve  denotes  the  commence- 
ment of  pressure:  the  upper  horizontal  part  corresponds  with  the  dura- 
tion of  the  pressure,  and  the  descent  with  the  rise  of  the  foot.  The 
lower  horizontal  part  of  the  curve  indicates  that  the  corresponding  foot 
is  in  the  air.  O  Pv.  Oscillations  of  the  pubis  from  above  downwards, 
that  is  vertically,  O  PA.  Oscillations  in  a  lateral  direction,  or  hori- 
zontally. It  is  evident  that  two  oscillations  in  the  vertical  direction 
correspond  with  a  single  horizontal  oscillation. 

The  person  who  walks,  follows  during  this  time  a  circular 
path,  pushing  before  him  the  arm  of  the  instrument,  to  which 
is  fixed  the  apparatus  which  is  to  experiment  on  the  vertical 
oscillations  of  the  pubis.    We  get  thus  the  tracing  repre- 


118 


ANIMAL  MECHANISM. 


sented  by  the  Hue  0  Pv  (fig.  22).  It  is  seen  that  the  pubis 
rises  at  the  middle  of  the  pressure  exerted  by  each  foot,  and 
sinks  at  the  instant  when  the  weight  of  the  body  passes  from 
one  foot  to  the  other. 

The  real  amplitude  of  these  oscillations  is  about  14  milli- 
metres, according  to  Mons.  Carlet.  This  movement,  however, 
varies  with  the  length  of  the  step ;  it  increases  with  it,  but 
this  increase  does  not  depend  on  the  maxima  of  the  curve 
being  more  elevated,  but  on  its  minima  being  lower. 

We  may  explain  these  phenomena  very  easily.  When  the 
body  is  about  to  quit  the  support  of  one  leg,  this  limb  is  in 
an  inclined  position,  and  the  result  of  its  obliquity  is  that  its 
superior  extremity  which  sustains  the  trunk  is  at  a  less  height. 
The  other  leg,  which  reaches  the  ground  at  this  instant,  is 
slightly  bent ;  it  will  soon  draw  itself  up,  and  thus  raise  the 
body  which  is  supported  by  it ;  but  in  this  movement,  the 
leg  describes  the  arc  of  a  circle  around  the  foot  resting  on  the 
ground ;  therefore,  in  the  series  of  successive  positions  which 
it  occupies,  the  body  rises  more  and  more  as  the  leg  which 
supports  it  approaches  the  vertical  position ;  it  sinks  again  as 
the  leg  becomes  oblique. 

We  can  easily  perceive  that  the  length  of  the  step  lowers 
the  trunk,  by  increasing  the  obliquity  of  the  legs.  Iudeed, 
the  constant  character  found  in  the  maxima  of  the  vertical 
oscillations  is  explained  by  this  fact,  that  the  leg,  when  ex- 
tended and  vertical,  constitutes  necessarily  a  constant  height 
— that  which  answers  to  the  maximum  of  the  elevation  of  the 
body. 

Horizontal  oscillations  of  the  body. — The  pubis,  since  that  is 
the  point  whose  displacement  we  are  now  studying,  is  carried 
alternately  from  left  to  right,  and  from  right  to  left,  at  the 
same  time  as  it  moves  vertically.  In  order  to  register  these 
movements,  we  make  use  of  a  lever-drum  arranged  in  such  a 
manner  that  the  membrane  is  forced  inwards  and  outwards 
alternately  by  the  lateral  movements  which  are  given  to  the 
lever.  During  this  time  the  registering  lever,  connected  with 
it  by  means  of  the  tube,  oscillates  vertically,  in  which  direc- 
tion alone  tracings  can  be  made  on  the  cylinder.  If,  in  the 
curve  which  is  traced,  the  elevation  corresponds  with  a  trans- 


WALKING. 


119 


ference  of  the  pubis  towards  the  right,  the  depression  will 
express  a  deviation  of  this  point  towards  the  left. 

The  experiment  gives  the  curve  OPIt  (fig.  22)  for  the 
tracing  of  the  horizontal  oscillations.  It  is  first  to  be  ob- 
served that  the  number  of  these  oscillations  is  only  half  that 
of  those  which  take  place  in  the  vertical  direction  ;  so  that 
the  body  is  carried  towards  the  right  side  at  the  moment  of 
the  maximum  of  elevation,  which  corresponds  with  the  middle 
of  the  pressure  on  the  right  foot,  and  towards  the  left  at  the 
middle  of  the  pressure  on  the  left  foot.  This  lateral  sway- 
ing of  the  trunk  is  the  consequence  of  the  alternate  passage 
of  the  body  into  a  position  sensibly  vertical  over  each  foot. 

If  we  would  give  an  idea  of  the  true  trajectory  of  the  pubis 
under  the  influence  of  these  two  oiders  of  oscillations  com- 
bined with  forward  movement,  we  must  construct  a  solid 
figure.  With  an  iron  wire  bent  in  different  directions,  we 
may  illustrate  very  clearly  this  trajec  tory.  Fig.  23  is  intended 
to  represent  the  perspeclive  view  of  this  twisted  iron  wire ; 
but  we  can  scarcely  expect  the  reader  to  comprehend  clearly 
this  mode  of  representation. 


Fia.  23. — Attempt  to  illustrate,  by  means  of  a  metallic  wire,  the  sinuous 
trajectory  passed  through  by  the  pubis.  To  understand  the  sketch  of 
this  solid  figure,  we  must  suppose  tlie  wire  to  be  close  to  the  observer 
at  its  left  hand  extremity,  while  it  is  removed  from  him  at  the  tight  ex- 
tremity. The  amplitude  of  the  oscillations  has  been  greatly  exaggerated 
to  render  them  more  intelligible. 

In  short,  according  to  the  formula  of  Mons.  Carlet,  the 
trajectory  of  the  pubis  may  be  inscribed  in  a  hollow  half- 
cylinder,  with  its  concave  portion  upwards,  at  the  base  of 


120 


ANIMAL  MECHANISM. 


which  lie  the  minima,  and  on  the  sides  of  which,  the  maxima 
terminate  tangentially. 

Forward  progress  of  the  body. — It  is  clear  that  during  the 
act  of  walking,  the  body  never  ceases  to  advance  ;  but  the 
forward  movement  has  not  always  the  same  velocity.  To 
appreciate  these  alternate  phases  of  acceleration  and  retarda- 
tion, it  is  necessary  to  employ  a  method  which  would  give  the 
measurement  of  the  space  passed  through  during  each  of  the 


Fig.  24.— Showing  two  successive  positions  of  the  arm  of  the  instrument, 
and  the  corresponding  positions  of  the  tracing  points  of  the  levers.  The 
arm  of  the  lever  being  three  metres  in  length,  and  the  radius  of  the 
cylinder  being  only  six  centimetres,  a  similar  angular  displacement  of 
the  person  walking,  and  of  the  style  which  writes,  will  correspond  with 
spaces  which  will  be  to  each  other  as  50  to  1. 


movements  in  the  act  of  walking,  and  which  would  also 
express  the  time  employed  in  passing  through  each  of  these 
spaces.  In  order  to  obtain  this  double  indication,  we  have 
recourse  to  the  following  method  : — 

It  is  necessary,  first,  to  ascertain  how  far  the  body  advances 
at  the  different  instants  of  the  act  of  walking.  This  measure 
of  the  spaces  passed  through,  is  obtained  by  inscribing  the 
curves  of  locomotion,  no  longer  on  a  cylinder  turning  with  a 
regular  motion,  but  on  an  immovable  one,  on  which  the 


WALKING. 


121 


registering  levers  are  displaced  by  a  quantity  proportionate  to 
the  space  passed  through. 

For  this  purpose  the  cylinder  is  placed  on  the  axis  round 
which  the  instrument  turns,  and  on  the  central  end  of  one  of 
these  revolving  arms  the  registering  instruments  are  fixed. 
The  ratio  of  the  radius  of  the  cylinder  to  that  of  the  circle 
described  by  the  person  walking,  allows  us  to  estimate  in  the 
tracings  the  length  of  the  space  passed  through  at  each  instant. 
This  ratio  was  50  to  1  in  our  experiments. 

Thus,  in  the  tracing  obtained,  if  from  one  point  to  another 
we  reckon  an  interval  of  a  centimetre,  this  corresponds  with 
50  centimetres  passed  over  on  the  ground  by  the  person 
walking.  This  first  notion  would  be  but  slightly  interesting 
in  itself,  since  it  would  teach  us  nothing  more  than  what  we 
learn  concerning  the  intervals  between  two  positions  of  the 
feet,  as  measured  on  the  ground.  The  impressions  left  by 
our  steps  on  soft  ground  would  furnish  in  a  very  simple 
manner  this  measurement.  But  if,  in  addition  to  this  know- 
ledge of  the  space  traversed,  the  tracing  gives  us  the  intima- 
tion of  the  time  passed  in  traversing  it,  we  are  provided 
with  a  method  of  estimating  the  rapidity  of  the  advance  of  the 
body  at  every  instant. 


D 


It 


Fig.  25.— D.  Tracing  of  the  impact  and  rise  of  the  right  foot,  furnished  by 
a  lever  subjected  at  the  same  time  to  10  vibrations  per  second.  It  U 
seen  that  the  vibrations  occupy  more  space  at  the  end  of  the  pressure 
of  the  foot ;  this  expresses  the  greatest  rapidity  of  the  advance  of  the 
body  at  this  moment.  The  same  acceleration  is  observed  at  the  end  of 
the  period  of  support  of  the  right  foot ;  tins  Is  explained  by  the  act  ion 
of  the  left  foot,  which  is,  at  th^s  moment,  at  the  end  of  its  pressure. 

Fig.  25  shows  (line  D)  the  tracings  of  the  impact  and  rise 
of  a  limb,  and  those  of  the  vibrations  of  a  chronograph 
inscribed  simultaneously.  To  obtain  these  tracings,  we  cause 
to  converge  at  the  same  time,  on  the  same  lever-drum,  two 
transmitting  tubes,  one  of  which  conveys  the  variations  of 


322  ANIMAL  MECHANISM. 

pressure  to  which  the  experimental  shoe  is  subjected  (fig.  1 9), 
and  the  other,  ten  vibrations  per  second  furnished  by  a  chrono- 
graphic  tuning-fork  of  large  size. 


Fig.  26. — A  large  tuning-fork  whose  vibrations  are  reduced  by  masses  of 
lead  to  It)  per  second,  acts  on  the  registering  lever  drum,  by  an  experi- 
mental drum  attached  to  one  of  its  branches.  This  also  receives  at  the 
same  time,  by  a  tube  with  two  branches,  the  influence  both  of  the  impact 
and  rising  of  the  foot  of  the  person  who  walks. 

Fig.  20  shows  how  these  instruments  are  arranged.  It  is 
seen  that  the  drum  will  be  affected  by  the  double  influence 


WALKING. 


123 


of  the  changes  in  the  pressure  of  the  foot  on  the  ground,  and 
of  the  vibrations  of  the  tuning-fork ;  and  this  produces  in  a 
single  tracing  the  interference  of  two  movements,  giving  at 
the  same  time  the  notion  of  the  space  traversed,  and  that  of 
the  time  employed  in  passing  over  it. 

In  order  to  analyse  this  tracing,  let  us  consider  only,  in  the 
first  place,  the  sinuous  curve  which  obeys  at  the  same  time 
the  tuning-fork,  and  the  experimental  shoe  on  the  right  foot  ; 
and  in  this  curve  let  us  only  examine  the  elevated  part — that 
which  corresponds  with  the  pressure  of  the  foot  upon  the 
ground.  We  see  that,  during  the  duration  of  this  pressure, 
the  style  has  passed  through  a  space  on  the  cylinder  measuring 
about  2  centimetres  ;  therefore,  as  the  displacement  of  the  style 
is  fifty  times  less  than  that  of  the  person  walking,  he  will  have 
advanced  about  one  metre  during  the  pressure  of  one  foot.  But 
while  he  traversed  this  metre,  he  did  not  advance  with  an 
uniform  velocity ;  in  fact,  during  the  first  half  of  this  distance, 
the  tuning- fork  made  about  four  vibrations,  whilst  in  the 
second,  it  has  scarcely  made  two  and  a  half.  Thus  the  foot 
which  presses  the  ground  with  a  force  increasing  from  the 
commencement  to  the  end  of  its  impact,  gives  the  body  au 
impulse  whose  velocity  equally  increases. 

During  the  rise  of  the  foot,  the  line  traced  by  the  tuning- 
fork  indicates  also  that  the  body  of  the  person  walking 
progresses  with  an  accelerated  motion.  That  is  easily  under- 
stood if  we  remember  that,  in  walking,  the  rise  of  one  foot 
corresponds  exactly  with  the  tread  of  the  other.  It  is,  there- 
fore, the  impact  of  the  left  foot  on  the  ground  which  gives  the 
body  of  the  walking  person  an  accelerated  motion,  which  is 
observed  during  the  rise  of  the  right  foot. 

This  method  appears  to  us  applicable  to  all  cases  in  which 
it  is  necessary  to  measure  the  relative  durations  of  different 
phases  of  movement. 

The  inequality  in  the  speed  of  the  man  who  walks  brings 
with  it  an  important  consequence.  When  a  man  drags  a 
load,  the  effort  which  he  makes  cannot  be  -constant ;  at  each 
foot-fall  a  redoubled  energy  is  produced  in  the  traction  that  is 
developed,  and  as  this  increase  of  effort  has  but  a  very  short 
duration,  a  seiies  of  shocks,  as  we  may  call  them,  occurs  at 


121 


ANIMAL  MECHANISM. 


each  instant.  But  we  know  that  these  shocks  are  very  un- 
favourable to  the  full  utilization  of  mechanical  force  ;  we  have 
explained  (page  49)  the  inconvenience  which  would  arise 
from  them  in  the  work  of  living  motive  agents,  and  the 
manner  in  which  these  shocks  are  lessened  by  the  elasticity 
of  muscular  fibre. 

Under  the  conditions  in  which  a  man  dragging  a  load  is 
placed,  if  he  is  attached  by  a  rigid  strap  to  the  mass  which 
he  has  to  draw,  the  shocks  of  which  we  have  spoken  will  be 
produced,  and  he  will  feel  their  reaction  on  his  shoulders.  In 
order  to  avoid  these  painful  jerks,  and  to  utilize  more  fully 
the  effort  which  he  makes,  we  have  placed  between  the  car- 
riage and  the  traction  strap  an  intermediate  elastic  portion, 
the  effect  of  which  has  answered  our  expectations. 

We  are  endeavouring  to  construct  analogous  contrivances, 
which  may  be  adapted  to  the  traces  of  ordinary  carriages,  so 
as  to  lessen  the  violence  of  the  pressure  on  the  collar,  and  to 
utilize  more  fully  the  strength  of  the  horse. 


CHAPTER  III. 

THE  DIFFERENT  MODES  OF  PROGRESSION  USED  BY  MAN. 

Description  of  the  apparatus  for  the  purpose  of  studying  the  various  modes 
of  progression  used  by  man — Portable  registering  apparatus  —Experi- 
mental apparatus  for  vertical  reactions— Walking— Running— Gallop 
— Leaping  on  two  feet  and  hopping  on  one — Notation  of  these  various 
methods— Definition  of  a  pace  in  any  of  these  kinds  of  locomotion 
— Synthetic  reproduction  of  the  various  modes  of  progression. 

The  principal  modes  of  progression  employed  by  animals, 
are  walking,  which  we  have  already  described  at  some  length 
as  far  as  it  relates  to  man,  running  at  different  rates  of  speed, 
the  gallop,  and  leaping  on  one  or  two  feet. 

The  act  of  walking  varies  according  to  the  nature  or  the 
slope  of  the  ground  ;  we  shall  have  to  treat  of  these  different 
influences. 

In  this  new  study  it  is  no  longer  possible  to  employ  the 


MODES  OF  PROGRESSION   USED   BY  MAN.  125 


apparatus  which  we  have  used  in  our  previous  researches. 
The  circular  and  horizontal  track  on  which  the  experimenter 
was  obliged  to  walk  must  be  exchanged  for  surfaces  of  every 
kind  and  of  every  slope. 

If  the  new  instruments  to  which  we  must  have  recourse 
leave  the  experimenter  more  liberty  in  his  movements,  they 
are,  on  the  other  hand,  relatively  less  complete  as  to  the  indi- 
cations which  they  furnish ;  therefore,  we  can  only  require 
from  them  two  kinds  of  indications ;  those  of  the  pressures  of 
the  feet  on  the  ground,  and  those  of  the  vertical  re-actions 
which  are  communicated  to  the  body  by  these  pressures. 

Fig.  27  shows  a  runner  furnished  with  apparatus  of  the 
new  construction.  He  wears  the  experimental  shoes  which 
we  have  already  described,  and  holds  in  his  hand  a  portable 
registering  instrument,  on  which  are  traced  the  curves  produced 
by  the  pressure  of  his  feet.  As  the  cylinder  of  this  instru- 
ment turns  uniformly,  the  curves  will  be  registered  in  propor- 
tion to  the  time,  and  not  to  the  space  traversed  during  each 
of  the  acts  by  which  this  curve  is  traced. 

In  order  to  facilitate  the  experiment,  and  to  allow  the 
apparatus  to  assume  a  uniform  motion  before  it  traces  on  the 
paper,  we  have  recourse  to  a  special  expedient.  The  points 
of  the  tracing  levers  do  not  touch  the  cylinder ;  but  in  order 
to  bring  them  in  contact  with  the  paper,  an  india-rubber  ball 
must  be  compressed.  As  soon  as  this  compression  ceases,  the 
points  retreat  from  the  cylinder,  and  the  tracing  is  no  longer 
produced.  In  fig.  27  the  runner  holds  this  bull  in  his  left 
hand,  and  compresses  it  with  his  thumb. 

In  addition  to  this,  the  runner,  in  order  to  obtain  the 
tracings  of  the  vertical  re-actions,  carries  on  his  head  an 
instrument  whose  arrangement  is  represented  in  fig.  28. 

It  is  an  experimental  lever- drum  fixed  on  a  piece  of  wood, 
which  is  fastened  with  moulding  wax  on  the  head  of  the  ex- 
perimenter, as  seen  in  fig.  27.  The  drum  is  provided  with 
a  piece  of  lead  placed  at  the  extremity  of  its  lever ;  this  mass 
acts  by  its  inertia. 

While  the  body  oscillates  vertically,  the  mass  of  lead  resists 
these  movements,  and  causes  the  membrane  of  the  drum  to 
sink  when  the  body  rises,  and  to  rise  when  the  body  descends. 
13 


MODES  OF  PROGRESSION   USED  BY  MAN.  127 


From  these  alternate  actions  a  current  of  air  results,  which, 
transmitted  by  a  tube  to  a  registering  lever,  shows  by  a  curve 
the  oscillatory  movements  of  the  body. 


Fio.  28. — Instrument  to  register  the  vertical  re-actions  during  the  various  paces. 

We  will  not  enter  into  the  details  of  the  experiments  which 
have  served  to  verify  the  exactitude  of  the  tracings  thus 
obtained;  they  consisted  in  adjusting  the  weight  of  the  disc 
of  lead  and  the  elasticity  of  the  membrane  of  the  drum, 
until  the  movements  given  to  the  apparatus  are  faithfully 
represented  in  the  tracing. 

We  will  call  step- curves  each  of  the  curves  formed  by  the 
pressure  of  a  foot  upon  the  ground,  and  we  will  designate  by 
the  name  of  ascending  or  descending  oscillations,  the  curve  of 
the  vertical  re-actions  on  the  body. 

1.  Of  walking. — We  have  already  pointed  out  the  distinc 
tive  character  of  walking  considered  as  one  of  the  modes  of 
progression  in  man.  We  have  said  that  the  body,  in  walking, 
never  leaves  the  ground,  and  that  the  footsteps  follow  each 
other  without  any  interval,  so  that  the  weight  of  the  body 
passes  alternately  from  one  foot  to  the  other. 

But  this  definition  cannot  apply  to  walking  on  an  inclined 
surface,  on  yielding  soil,  or  upstairs.  Being  obliged  to  pass 
rapidly  over  these  peculiar  conditions  of  walking,  we  will  only 
give  the  tracing  which  corresponds  with  the  act  of  mounting 
a  staircase  (fig.  29). 

It  is  to  be  remarked  that  the  step-curves  encroach  on  each 
other,  showing  that  each  foot  is  still  pressing  on  the  ground, 
when  the  other  has  already  planted  itself  on  the  next  step. 
Besides  this,  it  is  at  the  time  of  this  double  pressure  that 
the  lower  foot  exerts  its  maximum  force  ;  it  is  at  this  moment, 
in  fact,  that  the  work  is  produced  which  raises  the  body  to 
the  whole  height  of  a  step. 


128 


ANIMAL  MECHANISM. 


Nothing  like  this  is  observed  in  the  descent  of  a  staircase ; 
the  step-curves  cease  to  encroach  on  each  other,  and  succeed 
each  other  very  nearly  as  in  ordinary  walking  on  level 
ground. 


Fig.  29. — Tracing  produced  by  walking  upstairs.  D.  tracing  of  the  pressure 
and  rise  of  the  right  foot  (full  line  .  G.  tracing  of  the  left  foot  (dotted 
line).  It  is  seen  that  the  curves  produced  by  the  feet  encroach  one  on  the 
other,  and  that  the  maxima  of  the  pressures  of  the  feet  correspond  with 
the  end  of  the  pressures. 


2.  Of  running. — This  mode  of  progression,  more  rapid 
than  walking,  consists,  like  it,  in  alternate  treads  of  the  two 
feet,  whose  step-curves  follow  each  other  at  equal  intervals ; 
but  it  presents  this  difference,  that  in  running,  the  body 
leaves  the  ground  for  an  instant  at  each  step. 

Accordingly,  as  running  is  more  or  less  rapid,  different 
names  are  given  to  it;  those  of  the  gymnastic  march  and  the 
trot  present  no  utility  in  a  physiological  point  of  view ;  they 
correspond,  with  but  slight  variations,  to  running  at  various 
degrees  of  speed.  To  ascertain  the  principal  characters  of 
this  mode  of  progression,  it  is  only  necessary  to  analyse 
fig.  30. 


0 


Fig.  30. — Tracing  produced  by  running  (in  man).  D.  (curve  formed  by  a 
full  line),  impact  and  rise  of  right  to  >t.  G.  (dotted  line)  action  of  the  left 
foot.  O.  oscillations  and  vertical  re  actions  of  the  body. 

The  pressures  of  the  feet  are  more  energetic  than  in 
walking;  in  fact,  they  not  only  sustain  the  weight  of  the 


MODES  OF  PEOGRESSION  USED  BY  MAN.  129 


body,  but  impel  it  with  a  certain  speed  both  upwards  and 
forwards.  It  is  known  that  to  give  a  mass  a  rising  motion, 
a  greater  effort  must  be  exerted  than  would  be  sufficient 
6imply  to  sustain  it. 

The  duration  of  the  pressures  on  the  ground  is  less  than  in 
walking;  this  brevity  is  proportional  to  the  energy  with 
which  the  feet  tread  on  the  ground.  These  two  elements, 
force  and  brevity  of  pressure,  increase  generally  with  the 
speed  at  which  a  person  runs.  The  frequency  of  the  foot- 
falls increases  also  with  the  speed  of  the  runner ;  but  among 
the  various  kinds  of  running,  there  are  some  in  which  the 
extent  of  space  passed  over  in  a  given  time  depends  rather 
on  the  extent  of  each  pace  than  on  their  number. 

The  essential  character  of  running  is,  as  we  have  said,  the 
time  of  suspension  during  which  the  body  remains  in  the  air 
between  two  foot-falls.  Fig.  30  clearly  shows  the  suspension,  by 
the  interval  which  separates  the  descent  of  the  curves  of  the 
right  foot  from  the  ascent  of  the  curves  of  the  left  foot,  and 
vice  versa.  The  duration  of  this  time  of  suspension  seems  to 
vary  but  little  in  an  absolute  manner ;  but  if  we  compare  it 
with  the  speed  of  a  runner,  we  see  that  the  relative  time 
occupied  by  tnis  suspension  increases  with  the  speed  of  the 
course,  for  the  duration  of  each  tread  diminishes  in  proportion 
to  this  speed. 

How  is  this  suspension  of  the  body  at  each  impulse  of  the 
feet  produced  ?  We  might  think,  on  first  consideration,  that 
it  is  the  effect  of  a  kind  of  leap,  in  which  the  body  is  pro- 
jected upwards  in  so  violent  a  manner  by  the  impulse  of  the 
feet,  that  it  would  describe  in  the  air  a  curve,  in  the  midst  of 
which  it  would  attain  its  maximum  elevation  from  the  ground. 
In  order  to  convince  ourselves  that  such  is  not  the  case,  let  us 
make  use  of  the  apparatus  which  registers  the  re-actions  or 
vertical  oscillations  of  the  body. 

In  fig.  30  is  seen  (upper  line  O)  the  tracing  of  oscillations 
in  running.  This  trace  shows  us  that  the  body  executes  each 
of  its  vertical  elevations  during  the  downward  pressure  of  the 
foot,  so  that  it  begins  to  rise  as  soon  as  the  foot  touches  the 
ground ;  it  attains  its  maximum  elevation  at  the  middle  of  the 
pressure  of  this  foot,  and  begins  to  descend  again,  in  order  to 


130 


ANIMAL  MECHANISM. 


reach  its  minimum,  at  the  moment  when  one  foot  has  just 
risen,  and  before  the  other  has  reached  the  ground. 

This  relation  of  the  vertical  oscillations  to  the  pressure 
of  the  feet  shows  plainly  that  the  time  of  suspension  does  not 
depend  on  the  fact  that  the  body,  projected  into  the  air,  has 
left  the  ground,  but  that  the  legs  have  withdrawn  from  the 
ground  by  the  effect  of  their  flexion ;  and  this  takes  place  at 
the  very  moment  when  the  body  was  at  its  greatest  elevation. 

We  shall  have  again  to  recur  to  these  phenomena  when  we 
come  to  speak  of  the  paces  of  the  horse,  in  which  a  similar 
suspension  of  the  body  exists,  and  which  are  called  on  that 
account  elevated  paces. 

The  influence  of  the  different  inclinations  of  the  ground 
acts  in  nearly  the  same  manner  in  running  as  in  walking, 
with  this  difference,  that  in  running,  their  effects  are  generally 
greater. 

3.  Of  the  gallop. — In  the  modes  of  progression  described 
hitherto,  the  movement  of  the  limbs  is  regularly  alternate,  so 
that  the  succession  of  steps  is  made  at  equal  intervals. 
These  are  the  normal  kinds  of  human  locomotion ;  but  man 
can  imitate,  to  a  certain  extent,  by  the  movements  of  his  feet, 
those  periodically  irregular  cadences  which  are  produced  by  a 
horse  when  he  gallops.  Children,  in  their  amusements,  often 
imitate  this  mode  of  locomotion,  when  they  play  at  horses. 
This  abnormal  kind  of  motion  is  of  no  interest,  except  to 
explain  the  mechanism  of  the  gallop  in  quadrupeds. 

By  registering  together  the  step-curves  and  the  re-actions, 
it  is  seen  (fig.  31)  that  the  foot  placed  behind  is  the  first 
which  reaches  the  ground;  that  it  exerts  an  energetic  and 
prolonged  pressure,  towards  the  end  of  which  the  foot  in  front 
touches  the  ground  in  its  turn,  but  during  a  shorter  time ; 
after  which  there  is  a  considerable  period  of  suspension. 
Thus,  there  is  a  moment  when  the  two  feet  are  in  the  air. 

In  this  mode  of  progression,  the  re-actions  are  similar  in 
character,  in  some  respects,  to  the  pressures.  In  fact,  a  long 
re-action  (line  O)  is  produced,  in  which  we  recognise  the 
interference  of  two  vertical  oscillations,  the  second  of  which 
commences  before  the  first  has  finished.  After  this  re-action 
there  is  observed  a  lowering  of  the  curve,  whose  minimum 


MODES  OF  PROGRESSION  USED  BY  MAN.  131 


corresponds  with  the  moment  when  the  two  feet  are  in 
the  air. 


Fig.  SI. — Man  galloping  with  the  right  foot  first.  Step-curves  and  re- 
actions. There  is  an  encroachment  of  one  curve  over  the  other,  and  then 
a  suspension  of  the  body.  The  curve  O,  which  corresponds  with  the 
re-actions,  shows  the  effect  of  the  two  successive  impulses  exerted  on 
the  body  by  the  feet. 

4.  Of  leaping. — Although  leaping  is  not  a  sustained  mode 
of  progression  in  human  locomotion,  we  will  say  a  few  words 
about  it,  in  order  to  complete  the  series  of  the  movements 
which  man  is  able  to  execute. 

The  two  feet  being  joined  together,  we  can  make  a  series 
of  leaps,  and  advance  thus,  by  imitating  the  mode  of  locomo- 
tion of  some  birds,  or  of  certain  quadrupeds,  as  the  kangaroo. 


i  i 

i  1 

m  n 

r 

Fio.  32.— Leap  on  two  feet  at  once,  D  and  G.  The  line  R,  the  curve  of  re- 
actions, shows  that  the  maximum  of  elevations  corresponds  with  the 
middle  of  the  pressure  of  the  feet. 


The  apparatus  intended  to  illustrate  the  vertical  oscillations 
of  the  body,  being  placed  on  the  head  of  the  experimenter, 


132 


ANIMAL  MECHANISM. 


we  get  three  tracings  at  once  ;  those  of  the  pressures  of  the  two 
feet,  and  that  of  the  re -actions ;  these  furnish  fig.  32. 

We  see  here  that  the  maxima  of  the  curve  of  re-actions 
(line  R)  coincide  with  the  pressures.  Thus,  by  their  united 
energy,  the  two  legs  raise  the  body,  and  then  let  it  fall  again  at 
the  moment  when  they  bend  and  prepare  to  act  afresh. 

Hopping  on  one  foot  gives  the  tracings  (fig.  33)  which 
only  consist  in  the  pressure  and  rise  of  a  single  foot.  The 
elevations  of  the  body  coincide  with  the  step-curves  In  fact, 
when  the  speed  of  the  leap  is  lessened,  it  is  prolonged  more 
especially  at  the  period  of  the  pressure  of  the  foot  on  the 
ground,  that  of  suspension  remaining  very  nearly  constant. 


Fig.  33. — D,  series  of  hop*  on  the  right  foot.  The  duration  of  the  time 
of  suspension  remains  evidently  constant,  even  when  that  of  the  pressure 
of  the  foot  varies. 


In  certain  species  of  animals,  successive  leaps  constitute 
the  ordinary  mode  of  locomotion ;  it  will  be  interesting  to 
study  by  the  graphic  method  the  various  paces  of  these 
animals. 

NOTATION   OF  RHYTHM   IN  DIFFERENT  MODES  OF 
PROGRESSION. 

Among  the  characters  of  various  modes  of  progression,  it 
is  the  rhythm  of  the  impact  of  the  feet  which  is  the  most 
striking.  The  strokes  of  the  feet  upon  the  ground  give  rise 
to  sounds,  the  order  of  whose  succession  is  sufficient  for  a  per- 
son with  an  ear  accustomed  to  them  to  recognise  the  kind  of 
pace  which  originates  them.  We  will,  therefore,  endeavour 
to  establish  the  classification  of  the  various  paces  by  attending 
to  this  order  of  succession. 

In  order  to  give  the  figure  of  each  of  these  rhythms,  we  shall 
employ  the  musical  notation,  modified  so  as  to  furnish  at  the 


MODES  OF  PROGRESSION   USED  BY  MAN.  133 


same  time  the  notion  of  the  duration  of  each  pressure,  that  of 
the  foot  to  which  this  pressure  belongs,  and  also  the  length  of 
time  during  which  the  body  is  suspended.  This  notation  of 
rhythms  is  constructed  in  a  very  simple  manner  from  the 
tracings  furnished  by  the  apparatus. 


0 


Fia.  34. 


Let  us  return  (fig.  34)  to  the  curve  which  corresponds  with 
the  act  of  running  in  man.  Below  this  figure  let  us  draw 
two  horizontal  lines — 1  and  2  ;  these  will  form  the  staff  on 
which  will  be  written  this  simple  music,  consisting  only  of 
two  notes,  which  we  shall  call  right  foot,  left  foot.  From  the 
commencement  of  the  ascending  part  of  one  step  curve  be- 
longing to  the  right  foot,  let  us  let  fall  upon  the  staff  ;i  per- 
pendicular (a)  ;  this  line  will  determine  the  commencement  of 
the  pressure  of  the  right  foot.  A  perpendicular  (h)  let  fall 
from  the  end  of  the  curve  will  determine  where  the  pressure 
of  this  foot  ends.  Between  these  two  points,  let  us  trace  a 
broad  white  line ;  it  will  express,  by  its  length,  the  duration 
of  the  pressure  of  the  right  foot. 

A  similar  construction  made  on  the  step-curve  (No.  1)  will 
give  the  notation  of  the  pressure  of  the  left  foot.  The  nota- 
tions of  the  left  foot  have  been  shaded  with  oblique  lines  to 
avoid  all  confusion. 

Between  the  pressure  of  the  two  feet  there  is  found  to  he  silence 
in  the  rhythm;  that  is  to  say,  the  expression  of  that  instant 
of  the  course  when  the  body  is  suspended  above  the  ground. 


134 


ANIMAL  MECHANISM. 


If  we  note  in  this  manner  the  rhythms  of  all  the  paces  used 
by  man,  we  shall  obtain  a  synoptical  table  which  will  much 
facilitate  the  comparison  of  these  varied  rhythms.  Fig.  25 
represents  the  synoptical  notation  of  the  four  kinds  of  progres- 
sion, or  paces,  which  are  regularly  rhythmical,  and  in  which 
the  two  feet  act  alternately. 

Line  1  represents  the  notation  of  the  rhythm  of  the  walking 
pace.    This  is  the  principle  of  the  representation. 

The  pressure  of  the  right  foot  on  the  ground  is  represented 
by  a  thick  white  stroke,  a  sort  of  rectangle,  the  length  of 
which  corresponds  with  the  duration  of  that  pressure.  For 
the  left  foot  there  is  a  greyish  rectangle  shaded  with  oblique 
lines. 

These  alternations  of  grey  and  white  express,  by  their  suc- 
cession, that  in  walking  the  pressure  of  one  foot  succeeds  the 
other  without  allowing  any  interval  between  the  two. 


Fig.  35. — Synoptical  notation  of  the  four  kinds  of  progression  used  by  man. 


Line  2  is  the  notation  which  corresponds  with  the  ascent  of 
a  staircase.  It  is  seen,  agreeably  with  what  has  been  already 
explained  (fig.  29),  that  the  step-curves  encroach  on  each 
other,  and  that,  consequently,  the  body  during  an  instant  rests 
on  both  feet  at  once. 

Line  3  corresponds  with  the  rhythm  of  running.     After  a  * 
shorter  step-curve  of  the  right  foot  than  in  the  walking  pace, 
an  interval  is  seen  which  corresponds  with  the  suspension  of 
the  body ;  then  a  short  impulse  of  the  left  foot,  followed  by  a 
fresh  suspension,  and  so  on  continually. 

Line  4  answers  to  a  more  rapid  rate  of  running.  We  find  in 
it  a  shorter  duration  of  the  pressures,  a  longer  time  of  the 


MODES  OF   PROGRESSION    USED  BY  MAN. 


135 


suspension  of  the  body,  and  a  more  rapid  succession  of  the 
various  movements 


Fig.  36.— Notations  of  the  gallop.    1.  Left  gallop.    2.  Right  gallop. 

Fig.  36  is  the  notation  of  the  gallop  of  children,  a  mode  of 
progression  in  which  both  the  feet  do  not  move  in  the  same 
manuer.  In  this  figure,  line  1  represents  the  left  gallop — that 
is,  with  the  left  foot  always  forward.  It  is  seen  that  the  right 
foot  presses  on  the  ground  first;  then  the  left  falls  and  touches 
the  ground  for  a  shorter  time. 

Then,  there  occurs  a  suspension  of  the  body,  after  which 
the  right  foot  falls  afresh,  and  so  on.  The  time  of  the  simul- 
taneous pressure  of  both  feet  is  measured  according  to  the 
space  by  which  the  shaded  rectangle  rests  on  the  white  one. 

Line  2  is  the  notation  of  the  right  gallop  ;  that  is  to  say, 
when  the  right  foot  is  always  in  advance,  reaching  the  ground 
later  than  the  left.  Thus,  in  the  gallop,  the  bcdy  is  sometimes 
in  the  air,  sometimes  on  one  foot,  and  sometimes  supported 
by  two. 

Finally,  the  notations  represented  in  fig.  37  would  be: 
upper  line,  a  series  of  jumps  on  two  feet ;  lower  line,  a  series 
of  hops  on  the  right  foot  only. 


G 


Fio.  37.— (Upper  line),  notation  of  a  series  of  jumps  on  two  feet.  (Lower 
line),  notation  of  hops  on  right  foot.  It  la  seen  that  there  is  constancy 
in  the  durations  of  suspension,  notwithstanding  the  variabdity  of  tho 
pressures. 


Thie  method  of  representation  is  less  complete  than  the 


136 


ANIMAL  MECHANISM. 


curves  given  before,  for  it  does  not  indicate  the  phases  of 
variable  pressure  exerted  by  the  foot  upon  the  ground ;  but  it 
is  much  more  simple,  and  allows  the  two  modes  of  progression 
to  be  compared  much  more  easily  than  the  other.  It  will  be 
seen  farther  on,  when  speaking  of  quadrupedal  locomotion, 
that  the  complication  of  the  subject  renders  it  indispensable 
to  employ  this  very  simple  notation  of  the  rhythm  of  move- 
ment. 

Definition  of  a  pace  in  any  kind  of  progression  . — It  is  usually 
considered  that  a  pace  is  produced  by  the  series  of  movements 
which  are  executed  between  the  action  of  one  foot  and  that 
of  the  other,  whether  we  choose  for  the  commencement  of 
the  pace  the  instant  that  the  feet  reach  the  ground,  or  that 
when  they  rise  from  it.  Thus,  in  measuring  a  pace  on  the 
ground,  we  usually  take  as  its  length  the  distance  which 
separates  one  portion  of  the  print  of  the  right  foot  from 
a  similar  point  of  the  impression  made  by  the  left. 

We  shall  be  obliged  to  depart  from  this  usage.  Although 
we  regret  any  innovation,  yet  we  shall  consider  the  standard 
pace  only  as  half  a  pace,  and  we  shall  thus  define  it :  A  pace 
is  the  series  of  movements  executed  between  two  similar  positions  of 
the  same  foot — between  the  two  successive  treads  of  the  right 
foot,  for  example,  or  two  successive  elevations  of  the  left 
foot,  &c. 

In  the  same  manner  the  extent  of  a  pace  on  the  ground 
will  be  the  distance  which  separates  two  homologous  points 
taken  in  the  two  successive  impressions  of  the  same  foot. 
The  pace  is  estimated  in  this  manner  in  Mexico.  This  is  the 
only  method  of  counting  which  will  prevent  errors  in  the  very 
complicated  moments  of  quadrupedal  progression. 

SYNTHETIC   REPRODUCTION   OF  THE  MODES  OF  PROGRESSION 
EMPLOYED   BY  MAN. 

Since  we  have  completed  the  analysis  of  a  phenomenon  of 
which  we  now  seem  to  understand  all  the  details,  it  is  by 
synthesis  that  we  will  endeavour  to  construct  a  counter-proof. 
This  method  has  proved  very  useful  in  verifying  our  theories 
concerning  certain  physiological  actions,  as,  for  instance,  the 
circulation  of  the  blood.   It  consisted  in  representing,  by  arti- 


MODES  OF  PKOGKESSION  USED  BY  MAN.       J  37 


ficial  means,  the  movements  and  the  sounds  of  the  heart,  the 
arterial  pulsations,  &c,  and  we  thus  proved  the  correctness 
of  our  theories  as  to  the  nature  of  these  phenomena.  The 
same  method  will  serve  hereafter  to  verify  our  theories  of  the 
flight  of  insects  and  birds.  In  the  present  case  it  is  necessary 
to  represent,  according  to  the  data  afforded  by  analysis,  the 
movements  of  walking  and  of  the  other  paces  employed  by 
man. 

Every  one  knows  the  ingenious  optical  instrument  invented 
by  Plateau,  and  called  by  him  "  Phenakistoscope."  This 
instrument,  which  is  also  known  by  the  name  of  Zootrope, 
presents  to  the  eye  a  series  of  successive  images  of  persons  or 
animals  represented  in  various  attitudes.  When  these  atti- 
tudes are  co-ordinated  so  as  to  bring  before  the  eye  all  the 
phases  of  a  movement,  the  illusion  is  complete ;  we  seem  to 
see  living  persons  moving  in  different  ways. 

This  instrument,  usually  constructed  for  the  amusement  of 
children,  generally  represents  grotesque  or  fantastic  figures 
moving  in  a  ridiculous  manner.  But  it  has  occurred  to  us 
that,  by  depicting  on  the  apparatus  figures  constructed  with 
care,  and  representing  faithfully  the  successive  attitudes  of  the 
body  during  walking,  running,  &c,  we  might  reproduce  the 
appearance  of  the  different  kiuds  of  progression  employed 
by  man. 

Mons.  Carlet,  whose  remarkable  studies  of  walking  we  have 
before  quoted,  and  Mons.  Mathias  Duval,  professor  of  anatomy 
at  the  fecole  des  Beaux-arts,  have  carried  out  this  plan,  and, 
after  many  attempts,  have  arrived  at  excellent  results. 

Mons.  Duval  is  engaged  in  perfecting  his  diagram,  whicli 
furnishes  to  the  eye  sixteen  successive  positions  for  each  kind 
of  locomotion  employed  by  man.  Each  figure  is  carefully 
drawn  according  to  the  results  afforded  by  the  graphic  method. 
When  rotated  with  suitable  speed,  the  instrument  shows,  with 
perfect  precision,  the  different  movements  of  walking  or  run- 
ning. But  its  principal  advantage  is  that,  by  turning  it  lesa 
quickly,  we  cause  it  to  represent  the  movements  much  more 
slowly,  so  that  the  eye  can  ascertain  with  the  greatest  facility 
these  actions,  the  succession  of  which  cannot  be  apprehended  in 
ordinary  walking. 
14 


LS8 


ANIMAL  MECHANISM. 


CHAPTER  IV. 

QUADRUPEDAL  LOCOMOTION  STUDIED  IN  THE  HORSE. 

Insufficiency  of  the  senses  for  the  analysis  of  the  paces  of  the  horse  — 
Comparison  of  Duges — Rhythms  of  the  paces  studied  by  means  of  the 
ear — Insufficiency  of  language  to  express  these  rhythms —Musical 
notation  — Notation  of  the  amble,  of  the  walking  pace,  of  the  trot — 
Synoptical  table  of  paces  noted  according  to  the  definition  of  each  of 
them  by  different  authors— Instruments  intended  to  determine  by  the 
graphic  method  the  rhythms  of  the  various  paces,  and  the  re-actions 
which  accompany  them. 

Thebe  is  scarcely  any  branch  of  animal  mechanics  which 
has  given  rise  to  more  labour  and  greater  controversy  than  the 
question  of  the  paces  of  the  horse.  The  subject  is  one  of 
great  importance  to  a  large  number  of  persons  engaged  in 
special  pursuits,  but  its  extreme  complexity  has  caused  in- 
terminable discussions.  Any  one  who  proposed  at  the  present 
time  to  write  a  treatise  on  the  paces  of  the  horse,  would  have 
to  discuss  many  different  opinions  put  forward  by  a  great 
number  of  authors. 

While  reading  these  works,  on  which  so  much  sagacity  of 
observation  and  such  rigorous  reasoning  have  been  expended, 
one  is  astonished  to  find  that  the  greater  number  of  these 
writers  are  not  agreed  in  their  definitions  of  the  paces.  This 
disagreement  in  similar  observers  can  only  be  accounted  for 
on  the  principle  of  the  insufficiency  of  the  means  at  their 
disposal  to  enable  them  to  analyse  the  very  complex  and  rapid 
movements  of  the  horse.  The  difficulty  of  expressing  in 
words  the  rhythms  and  the  durations  of  these  various  move- 
ments adds  still  more  to  the  confusion.  When  a  horse  is 
running,  and  passing  from  one  kind  of  motion  to  another ; 
when  he  moves  his  limbs  with  a  rapidity  which  makes  one 
dizzy,  and  according  to  the  most  varied  rhythms,  how  can  we 
appreciate  and  describe  faithfully  all  these  actions  ?  It  would 
be  as  easy  a  task,  after  looking  at  the  fingers  of  a  pianict 


PACES  OF  THE  HORSE. 


139 


when  running  over  the  keys,  to  try  and  describe  the  move- 
ments which  have  just  been  executed. 

Still,  in  the  midst  of  this  confusion,  it  has  been  found 
possible,  by  observation  alone,  to  establish  certain  divisions 
which  singularly  simplify  the  study.  Thus,  certain  paces  give 
to  the  ear  a  rhythm  in  which  the  strokes  of  the  hoofs  succeed 
each  other  at  sufficiently  regular  intervals;  others,  such  as  the 
different  kinds  of  gallop,  offer  an  irregular  rhythm,  recurring 
at  periodical  times.  These  latter  paces  are  the  most  difficult 
to  analyse. 

But  if  we  observe  a  horse  either  at  a  walking  pace,  ambling, 
or  trotting,  and  if  we  concentrate  our  attention  on  the  anterior 
limbs  alone,  or  on  the  posterior  ones,  we  perceive  that  the 
rhythm  of  the  impacts  and  elevations  of  the  right  and  left 
foot  entirely  resemble  those  of  the  feet  of  a  man  walking  or 
running  more  or  less  quickly.  The  alternation  of  the  strokes 
of  the  feet  is  perfectly  regular,  if  the  horse  be  not  lame  of 
one  of  the  limbs  under  observation. 

If  we  then  pass  to  the  comparison  of  the  movements  in  the 
two  fore  and  hind  legs  on  the  same  side,  we  see  that  the  two 
feet  on  the  right  side,  for  example,  make  the  same  number  of 
steps,  and  that  if  one  of  them  strikes  the  ground  at  a  greater 
or  less  interval  before  the  other,  this  is  preserved  as  long  as 
the  same  pace  is  continued.  Add  to  this  that  the  length  of 
the  step  is  the  same  for  both  the  fore  and  hind  limbs,  of 
which  fact  we  may  convince  ourselves  by  seeing  that  these 
two  feet  always  leave  on  the  ground  prints  situated  at  the 
same  distance  from  each  other.  In  general,  the  hind- foot 
covers  the  print  left  by  the  corresponding  fore-foot ;  if  the 
priuts  be  not  covered,  they  preserve  always  the  same  distance 
from  each  other.  Thus,  the  steps  of  the  fore  and  hind  legs 
are  of  the  same  number  and  the  same  extent ;  these  facts 
have  not  escaped  former  observers. 

Duges  has  compared  the  quadruped  when  walking  to  two 
men  placed  one  before  the  other,  and  following  each  other. 
According  as  these  two  persons  (who  ought  both  to  take  the 
same  number  of  steps),  move  their  limbs 'simultaneously,  or 
alternately ;  according  as  the  man  in  front  executes  his  move- 
ments more  quickly  or  more  slowly  than  the  one  behind,  we 


140 


ANIMAL  MECHANISM. 


see  all  the  rhythms  of  the  movements  which  eharac  erize 
the  different  paces  of  the  horse  reproduced. 

Every  one  has  seen  in  the  circus  or  the  masquerade  those 
figures  of  animals  whose  legs  are  formed  by  those  of  two  men 
with  their  bodies  concealed  in  that  of  the  horse.  This  gro- 
tesque imitation  bears  a  striking  resemblance  to  the  animal, 
when  the  movements  of  the  two  men  are  well  co-ordinated,  so 
as  to  reproduce  the  rhythms  of  the  paces  of  a  real  quadruped. 

In  the  examination  of  the  tracings  furnished  by  the  graphic 
method  when  applied  to  the  paces  of  the  horse,  we  may  have 
recourse  to  the  theory  propounded  by  Du<;es;  we  shall  then 
find  the  curves  furnished  by  human  locomotion  twice  repeated. 
We  shall  see  that  the  difference  between  one  pace  and  another 
consists  in  the  manner  in  which  the  footfalls  of  the  hind  leg 
of  a  horse  succeed  each  other,  with  relation  to  those  of  the 
fore  leg  on  the  same  side.  But  this  determination  of  the 
order  of  the  succession  of  footfalls  presents  singular  diffi- 
culties, even  for  the  most  skilful  observers. 

Many  attempts  have  been  made  to  bring  to  perfection  the 
means  of  observation,  and  to  remedy  the  insufficiency  of 
language  in  the  description  of  the  observed  phenomena. 
Long  since,  the  rhythm  of  the  steps  according  to  the  sounds 
which  they  produce  has  been  substituted  for  their  examination 
by  means  of  the  eye.  The  ear,  in  fact,  is  better  adapted  than 
the  eye  to  distinguish  the  rhythms  or  relations  of  succession. 
To  ascertain  the  order  in  which  each  limb  strikes  the  ground, 
certain  experimenters  have  attached  to  the  legs  of  the  horso 
bells  of  different  tones,  which  can  be  easily  distinguished  from 
each  other. 

A  point  which  has  been  better  ascertained  with  respect  to 
the  locomotion  of  the  horse,  is  the  determination  of  the  space 
passed  over  on  the  ground  during  each  of  the  various  kinds 
of  paces.  This  spnce  has  been  directly  measured  by  means 
of  the  distance  between  the  prints  of  the  feet  left  on  the 
ground.  To  render  the  distinction  between  the  footprints 
more  easy,  each  of  the  animal's  feet  has  been  shod  in  a 
different  manner.  Besides  this,  observers  have  studied  the 
proportion  which  exists  between  the  height  of  the  animal  and 
the  length  of  its  various  paces.    All  those  who  have  made 


PACES  OF  THE  HORSE. 


141 


any  progress  in  this  interesting  study  have  arrived  at  it  by 
the  employment  of  rigorous  methods  of  observation. 

On  the  other  hand,  the  manner  of  expressing  the  observed 
phenomena  has  occupied  the  attention  of  different  authors. 
Almost  all  have  had  recourse,  with  great  advantage,  to  the 
use  of  drawings,  but  have  agreed  but  little  in  their  mode  of 
representing  the  successive  actions  which  characterise  the 
different  paces.  The  most  perfect  kind  of  representation 
is  that  employed  during  the  last  century  by  Vincent  and 
Goiffon.*  A  sort  of  musical  staff,  composed  of  four  lines, 
served  to  note  the  instant  of  each  impact  of  the  four  feet,  and 
the  duration  of  the  succeeding  pressures  on  the  ground.  This 
notation  resembles,  to  a  certain  degree,  that  which  we  have 
employed  to  represent  the  different  rhythms  of  human  loco- 
motion, and  which  will  hereafter  serve  to  explain  the  various 
paces  of  the  horse.  But  we  must  not  forget  that  the  method 
of  Vincent  and  Goiffon  only  expressed  a  succession  of  move- 
ments observed  by  the  sight  or  the  ear,  and  that  it  realised  no 
greater  exactitude  than  that  of  the  individual  observer. 

Our  registering  instruments  resolve  the  double  problem  of 
analysing  with  fidelity  the  acts  which  the  senses  could  not 
accurately  appreciate,  and  expressing  clearly  the  result  of  this 
analysis. 

Before  we  describe  our  experiments,  we  shall,  in  order  that 
the  reader  may  understand  their  utility,  try  to  present  a 
summary  of  the  present  state  of  the  science,  and  to  show  what 
disagreement  exists  on  various  points  among  different  authors. 
As  the  standard  definitions  are  not  always  easy  to  be  under- 
stood, we  shall  add  to  them  the  notation  of  each  of  the  paces, 
trusting  that  this  method  of  representation  will  render  them 
more  intelligible,  and  especially  more  easy  to  be  compared 
with  each  other. 

Notation  of  the  various  paces  of  the  horse. — Recurring  to  the 
comparison  used  by  Duges,  let  us  represent  the  horse  as  com- 
posed of  two  bipeds  walking  one  behind  the  other.  We  must 
determine  the  manner  in  which  the  rise  and  fall  of  the  feet 

*  Memoire  artificielle  des  principes  relntifs  a  la  fiddle  representation  des 
animaux,  tant  en  peintnre  qu'en  sculpture.    Altord,  1769. 


142 


ANIMAL  MECHANISM. 


succeed  each  other,  in  each  of  the  persons  supposed  to  be 
walking*. 

Of  the  amble. — Let  us  take  the  simplest  case,  in  which  the 
two  persons  walking  steadily  go  through  the  same  movements 
at  the  same  time.  If  we  represent,  by  the  notation  before 
employed,  the  movements  of  these  two  men,  placing  at  the  top 
the  notation  which  belongs  to  the  foremost,  and  below  it  that 
of  the  hindmost,  we  shall  have  the  following  figure  : — 


Fio.  38.— Notation  of  a  horse's  amble. 


The  footfalls  of  the  right  and  left  foot  being  produced  at 
the  same  time  by  the  person  walking  in  front  and  by  him  who 
follows,  must  be  represented  by  similar  signs  placed  exactly 
over  each  other.  Thus,  in  the  paces  of  the  horse,  this 
agreement  between  the  movements  of  the  fore  and  hind  limbs 
belongs  to  the  amble.  The  notation  (fig.  38)  will  be  that  of 
a  horse's  amble ;  the  upper  line  referring  to  the  movements 
of  the  fore  quarters  of  the  animal,  and  the  lower  line  to  the 
hind  limbs. 

The  standard  definition  is  the  following  :  "  The  amble  is  a 
kind  of  pace  characterised  by  the  alternate  and  exclusive 
action  of  two  lateral  bipeds."  Authors  are  entirely  agreed  on 
this  point.  Let  us  add  that  in  the  amble  the  ear  perceives 
only  two  beats  at  each  pace,  the  two  limbs  on  the  same  side 
striking  the  ground  at  the  same  instant.  In  the  notation 
these  two  sounds  are  marked  by  vertical  lines  joining  the  two 
synchronous  impacts. 

In  the  amble  the  pressure  of  the  body  on  the  ground  is 
said  to  be  lateral,  as  the  two  limbs  on  one  side  only  are  in 
contact  with  the  ground  at  the  same  time. 

Of  the  walking  pace. — According  to  the  definition  of  the 
greater  number  of  authors,  the  walking  pace  consists  in  an 
equal  succession  of  impacts  of  the  four  feet,  which  strike  the 
ground  in  the  following  order :  if  the  right  foot  be  considered 
as  moving  first,  we  shall  have  the  following  succession — right 
fore-foot,  left  hind  foot,  left  fore-foot,  and  then  right  hind-foot. 


PACES  OF  THE  HORSE. 


143 


To  express  this  succession  of  movements  of  the  two  persons 
walking,  it  is  only  necessary  to  alter  the  place  of  the  signals  of 
the  hind  feet  with  respect  to  those  of  the  fore  feet.  We  shall 
obtain  the  rhythm  indicated  by  authors  by  causing  the  signals 
of  the  hind  feet  to  slip  towards  the  left,  which  will  give  the 
following  figure : — 


Fig.  39.— Notation  of  the  horse's  walking  pace 


It  is  seen,  therefore,  that  when  compared  with  the  amble, 
the  walking  pace  consists  in  an  anticipation  of  the  hinder 
limbs,  whose  footfalls  precede  those  of  the  corresponding  fore 
limbs  by  the  half  of  the  duration  of  one  of  their  pressures 
on  the  ground. 

If  the  notations  be  read  from  left  to  right,  like  ordinary 
writing,  it  is  evident  that  each  sign  situated  farther  to  the 
left  than  another  precedes  it  in  order  of  succession.  Thus, 
in  fig.  39,  the  impact  of  the  right  hind-foot  precedes  that  of 
the  right  fore-foot.  But  as  it  is  of  little  consequence,  in  the 
series  of  successive  acts  of  the  same  kind  of  pace,  whether  we 
choose  one  instant  rather  than  another  as  the  point  of  depar- 
ture, we  shall  always  take  as  the  commencement  the  impact 
of  the  right  fore-foot. 

The  ear  distinguishes  four  beats,  separated  by  regular 
intervals,  each  of  which  is  indicated  in  the  notation  by  a 
vertical  line.  Finally,  the  body  rests  on  the  ground  twice 
laterally  and  twice  diagonally  during  one  entire  pace.  It  is 
easy  to  ascertain  this  by  looking  at  fig.  39,  in  which,  after 
the  first  impact,  the  body  rests  on  the  right  feet  (lateral  biped 
L)  ;  after  the  second  impact,  on  the  right  foot  in  front,  and 
the  left  foot  behind  (diagonal  biped  D),  &c. 

But  this  notation  only  expresses  the  theory  of  the  most 
extended  pace.  The  equality  of  intervals  between  the  strokes 
of  the  feet  is  not  admitted  by  all  writers.    We  shall  see,  in 


144 


ANIMAL  MECHANISM. 


the  course  of  our  experiments,  that  the  walking  pace,  in  fact, 
may  present  different  rhythms. 

Of  the  trot. — The  notation  of  the  trot  is  obtained  by  a 
more  decided  anticipation  of  the  hinder  limbs,  each  of  which 
will  have  entirely  completed  its  pressure  on  the  ground, 
and  begun  to  rise  at  the  moment  when  the  fore-leg  on  the 
,  same  side  has  completed  its  stroke.  Fig.  40  expresses  the 
absolute  alternation  of  the  two  persons  supposed  to  be 
walking. 


Fig.  40. — Notation  of  a  horse's  trot 


Authors  agree  also  on  this  point,  that  in  the  trot,  the 
limbs  which  act  together  are  associated  in  diagonal  pairs. 

The  ear  perceives  but  two  sounds  of  the  hoofs,  as  in  the 
amble,  but  with  this  difference,  that  it  is  always  a  right  and 
left  foot  together,  and  not  two  feet  on  the  same  side,  which 
produce  each  sound. 

The  notation  also  shows  that  the  pressure  of  the  body  on  the 
ground  is  always  diagonal.  What  it  does  not  express  is,  that 
between  successive  pressures,  the  body  of  the  animal  is,  for  an 
instant,  suspended  in  the  air.  This  suspension  arises  from 
the  fact  that  the  trot  is  not  a  walking,  but  a  running  pace,  and 
that  to  represent  it  faithfully  we  must  place  together  two 
notations  similar  to  that  which  is  represented  in  fig.  34. 

We  have  designedly  omitted  the  time  of  suspension  in  the 
former  notation ;  it  would  have  rendered  a  difficult  subject 
still  more  complicated.  Besides,  this  suspension  does  not 
always  take  place  ;  certain  horses  have  a  low  trot,  which  has 
nothing  to  characterise  it  except  its  rhythm  in  double  time 
and  the  diagonal  impacts  of  the  feet. 

We  will  not  fatigue  the  reader  by  detailing  the  definition 
of  all  the  paces  admitted  by  different  authors.  We  shall 
merely  present  in  a  synoptical  table  the  series  of  notations 
which  correspond  with  them.  In  this  table  (fig.  41)  it  is 
seen,  that  all  the  lower  paces  may  be  considered  as  derived 


PACES  OF  THE  HORSE. 


145 


from  the  amble,  aiid  that  if  we  wished  to  make  a  methodical 
classification,  we  should  group  them  in  a  series  of  which  the 
amble  would  be  the  first  term,  and  all  the  other  terms  would 
be  obtained  by  means  of  an  increasing  anticipation  of  th 
movements  of  the  hinder  limbs.  Fig.  41  represents  this  series. 
In  the  notation  of  each  kind  of  pace,  we  have  left  on  the  same 
vertical  the  impact  of  the  right  fore-foot,  which  we  shall  choose 
as  the  commencement  of  each  pace,  and  which  will  serve  as 
a  point  of  reference  to  characterise  each  kind  of  locomotion. 

This  table,  prepared  from  different  treatises  on  the  horse, 
represents  as  faithfully  as  we  have  been  able  to  depict  it, 
that  which  each  author  admits  as  constituting  each  particular 
kind  of  pace.  The  explanatory  notes  show  the  disagreement 
which  exists  between  the  various  theories  relative  to  the  suc- 
cession of  movements  which  characterise  each  of  them.  Thus 
we  see,  that  with  the  exception  of  the  amble,  on  which  all 
are  agreed,  all  the  other  kinds  of  paces  are  defined  in  a 
different  manner  by  various  authors.  Thus,  the  notation 
No.  2,  which,  according  to  Merche,  would  correspond  with 
the  broken  amble,  would  be,  according  to  Bouley,  the  expres- 
sion of  the  high  step,  or  the  pace  of  Norman  ponies;  while 
this  same  Norman  pace  would  be,  according  to  Lecoq,  that 
which  is  represented  in  No.  9.  We  also  see  that  the  notation 
of  No.  3  would  correspond,  according  to  Merche,  witli  the 
ordinary  step  of  a  pacing  horse,  while  Bouley  would  consider  it 
as  a  broken  amble,  and  Lecoq  the  traquenade  ;  which  traquenade, 
according  to  Merche,  would  not  differ  from  the  pace  repre- 
sented by  the  notation  No.  10.  The  ordinary  walking  pace 
itself  is  not  understood  in  the  same  manner  by  different 
writers,  and  if  the  greater  part  of  them,  with  Vincent  and 
Goiffon,  Colin,  Bouley,  &c,  admit  in  this  pace  a  succession  of 
impacts  at  unequal  intervals,  it  is  to  be  observed  that  the 
theory  of  Lecoq  and  Raabe,  concerning  the  normal  pace,  in- 
different. 

This  disagreement  can  easily  be  explained :  first,  the 
observation  of  these  movements  is  very  difficult ;  then,  each 
pace  must  naturally  present,  according  to  the  conditions 
under  which  it  is  studied,  the  different  forms  which  eacli 
writer  has  arbitrarily  taken  as  the  type  of  the  normal  walking 


Fig.  41. 


— Synoptical  notations  of  the  paces  of  the  horse,  according  to 
various  writers.— See  Description  at  the  foot  of  page  147. 


TACES  OF  THE  HORSE. 


147 


pace.  Each  one  has  suffered  himself  to  be  guided  in  this 
respect  by  theoretical  considerations.  Those  who  admit  equal 
intervals  between  the  four  footfalls,  have  thought  that  they 
found  in  this  type  more  clearness  and  a  more  decided  dis- 
tinction between  the  amble  and  the  trot.  The  other  writers 
have  attempted  the  realisation  of  a  certain  ideal  in  the  kind 
of  pace  which  served  them  as  a  type.  For  Raabe,  it  was  the 
maximum  of  stability,  which,  according  to  his  theory,  is 
obtained  when  the  weight  of  the  body  rests  longer  on  the  two 
diagonal  feet  than  on  the  two  lateral  feet ;  whence  arises  the 
choice  of  the  type  represented  by  the  notation  No.  6.  Lecoq, 
thinking,  on  the  contrary,  that  the  most  rapid  pace  is  the  best, 
has  chosen  as  his  type  the  pace  in  which  the  body  rests  longer  on 
the  two  lateral  feet  than  on  the  diagonal  ones  (notation  No.  4). 

Whatever  may  be  the  value  of  these  considerations,  of 
which  practical  men  alone  can  judge,  it  seems  to  us  that  the 
physiologist  must  first  of  all  endeavour  to  search  for  facts,  and 
must  take  simply  such  types  as  experiment  may  reveal  to  him. 
It  is  for  this  purpose  that  the  investigations  have  been  made  with 
registering  apparatus,  the  result  of  which  will  now  be  given. 

APPARATUS   INTENDED   FOR  THE  STUDY   OF  THE  MODES 
OF  LOCOMOTION   OF  THE  HORSE. 

For  the  experimental  shoe  employed  in  the  experiments  made 
on  man  has  been  substituted,  on  the  horse,  a  ball  of  india- 
rubber  filled  with  horsehair,  and  attached  to  the  horse's  hoof 
by  a  contrivance  which  adapts  it  to  the  shoe. 


Description  of  Fiq.  4L 
No.  L   Amble,  according  to  all  writers. 
No  2  1  Broken  amble,  according  to  Merche. 
(  High  step,  according  to  Bouley. 

(  Ordinary  step  of  a  pacinrt  horse,  according  to  Mazuro. 
No.  3.  •<  Broken  amble,  according  to  Bouley. 

(  Traquenade,  according  to  Locoq. 
No.  4.    Normal  walking  pace,  according  to  Lecoq. 

No.  5.   Normal  walking  pace  (Bouley,  Vincent  and  Goiffon,  Solbysel,  Colin). 
No.  6.    Normal  walking  pace,  according  to  Raabe. 
No.  7.    Irregular  trot  (trot  decousu). 

No  8.    Ordinary  trot  (In  the  figure,  it  is  supposed  that  the  animal  trots  with- 
out leaving  the  ground,  which  occurs  but  rarely.    The  notation  onl}  takes  into 
account  the  rhythm  of  the  impacts  of  the  feet.) 
No.  9.    Norman  pace,  from  Lecoq. 
No.  10.  Traquenade,  from  Merche. 


148 


ANIMAL  MECHANISM. 


By  turning  an  adjusting  screw  we  fix  if,  to  the  horse-shoe 

by  three  catches,  which 
keep  the  instrument  se- 
curely fastened.  A  strong 
band  of  india-rubber  passes 
over  the  apparatus  (fig.  42), 
and  keeps  in  its  place  the 
ball  filled  with  horse-hair, 
so  as  to  allow  it  to  rise 
slightly  above  the  lower 
surface  of  the  hoof.  When 
the  foot  strikes  the  ground, 
the  india-rubber  ball  is 
compressed,  and  drives  a 
part  of  the  confined  air 
into  the  registering  instru- 
ments. When  the  foot  is 
raised,  the  ball  recovers  its 
form,  and  draws  again  into 
its  interior  the  air  whick 

Fig.  42.— Experimental  apparatus  to  show      the  pressure  had  expelled. 

gSundSSUre  °f  the  h°rSe 8  W  °n  thG    Tliese    instruments  soon 

wear  out  on  the  road,  but 
will  last  during  some  time  on  the  artificial  soil  of  the  riding- 
school. 

For  experiments  which  we  have  made  on  ordinary  roads, 
we  have  had  recourse  to  an  instrument  represented  in  fig.  43. 

To  the  leg  of  the  horse  just  above  the  fetlock  joint  is 
attached  a  kind  of  leather  bracelet  fastened  by  straps.  In  front 
of  this  bracelet,  which  furnishes  a  solid  point  of  resistance, 
are  placed  various  pieces  of  apparatus.  There  is,  first,  a  flat 
box  of  india-rubber  firmly  fixed  in  front  of  the  bracelet ;  this 
box  communicates,  by  a  transmission  tube,  with  the  registering 
apparatus.  Every  pressure  exerted  on  the  box  moves  the 
corresponding  registering  lever.  It  is  evident  that  all  the 
movements  of  the  horse's  foot  are  shown  by  pressures  on  the 
india-rubber  box,  and  are  immediately  signalled  by  the  regis- 
tering levers. 

For  this  purpose,  a  plate  of  copper,  inclined  about  45°,  is 


DESCRIPTION  OF  APPARATUS. 


U9 


connected  at  its  upper  extremity  with  a  kind  of  hinge,  whilst 
its  lower  end  is  fastened  by  a  solid  wire  to  the  upper  face  of 
the  india-rubber  box,  on 
which  it  presses  by  means 
of  a  flat  disc.  On  a  wire 
parallel  to  the  slip  of 
copper  slides  a  ball  of  lead, 
the  position  of  which  can 
be  varied  in  order  to  in- 
crease or  diminish  the 
pressure  which  this  jointed 
apparatus  exerts  on  the 
india-rubber  box. 

The  function  of  this 
apparatus  is  analogous  with 
that  of  the  instrument  re- 
presented in  fig.  28,  in- 
tended to  show  the  re- 
actions which  are  produced 
in  various  kinds  of  loco- 
motion ;  only  the  inclina- 
tion of  the  oscillating  por- 
tions allows  them  to  act  on 
the  membrane  during  the 
movement  of  the  elevation, 
the  descent,  and  the  hori- 
zontal progress  of  the  foot. 

When  the  hoof  meets 
the  ground  the  ball  has  a 
tendency  to  continue  its 
motion,    and    compresses     Plo  4S  _Appsimtua  to  give  the  signal-  of 

with  force  the  india-rubber         tli0  pressure  and  rise  of  the  horse's  hoof. 

box.    When  the  foot  rises, 

the  inertia  of  the  ball  produces  in  its  turn  a  compression 
by  a  kind  of  mechanism  already  described  with  reference  to 
fig.  28. 

Through  the  kindness  of  Mons.  Pellier,  we  have  been  able 
to  experiment  on  several  horses,  ridden  by  himself,  while 
holding  in  his  hand  the  registering  instruments. 
15 


150 


ANIMAL  MECHANISM. 


When  the  horse  had  his  feet  furnished  with  the  india-rubber 
boxes  which  have  just  been  described,  thick  transmitting 
tubes  not  easily  crushed  were  fitted  to  these  receptacles. 
These  tubes  are  usually  fastened  by  flannel  bands  to  the  legs 
of  the  animal,  and  thence  directed  to  a  point  of  attachment 
at  the  level  of  the  withers ;  they  are  then  continued  to  the 
registering  apparatus,  which  has  been  already  described 
in  the  experiments  on  biped  locomotion.    The  registrar  now 


Fig.  44.— This  figure  represents  a  trotting  horse,  furnished  with  the  different 
experimental  insti  uments  ;  the  horseman  carrying  the  register  of  the 
pace.  On  the  withers  and  the  croup  are  instruments  to  show  the  re- 
actions. 


carries  a  great  number  of  levers ;  he  must  have  four  at 
least — one  for  each  of  the  legs,  and  usually  two  other  levers 
which  receive  their  movements  of  re-action  from  the  withers 
and  the  croup.  Similar  kinds  of  apparatus  to  those  repre- 
sented in  fig.  28  are  employed  for  this  purpose. 

The  rider  carries  by  the  handle  a  portable  registering  in- 
strument, to  which  all  the  levers  give  their  signals  at  once ; 
the  hand  which  holds  the  reins  is  also  ready  to  compress  a 


PACES  OF  THE  HORSE. 


151 


hall  of  india-rubber  at  the  moment  when  the  horseman  wishes 
the  tracings  to  commence.  Fig.  44  represents  the  general 
arrangement  of  the  apparatus  at  the  moment  when  the  rider 
is  about  to  collect  the  graphic  signals  of  any  particular  pace. 


CHAPTER  V. 

EXPERIMENTS  ON  THE  PACES  OF  THE  HORSE. 

Double  aim  of  these  experiments  :  determination  of  the  movements  under 
the  physiological  point  of  view,  and  of  the  attitudes  with  reference 
to  art. 

Experiments  on  the  trot — Tracings  of  the  pressures  of  the  feet  and  of  the 

re-actions— Notation  of  the  trot— Piste  of  the  trot—  Representation 

of  the  trotting  horse. 
Experiments  on  the  walking  pare — Notation  of  this  kind  of  motion  ;  its 

varieties — Piste  of  the  walking  pace— Representation  of  a  pacing 

horse. 

The  aim  of  these  experiments  is  twofold ;  as  far  as 
physiology  is  concerned,  we  derive  from  them  the  expression 
of  the  duration,  actions,  and  re-actions  of  each  pace,  the 
energy  and  duration  of  each  movement,  and  the  rhythm  of 
their  succession.  But  the  artist  is  no  less  interested  in 
knowing  exactly  the  attitude  which  corresponds  with  each 
movement,  in  order  to  represent  it  faithfully  with  the  various 
poses  which  characterise  it.  All  these  details  are  furni>hod 
by  the  registering  apparatus ;  the  artist  need  fear  no  error  if 
he  conform  his  sketches  to  the  indications  furnished  by  the 
tracings  made  by  the  instrument. 

The  remarkable  work  of  Vincent  and  Goiifon  was  expressly 
intended  to  establish  principles  relative  to  the  faithful  repre- 
sentation of  the  horse.  We  shall  borrow  some  things  from 
this  book,  which  seems  to  have  been  too  much  forgotten,  and 
not  to  have  exercised  upon  art  the  influence  that  might  havo 
been  expected.  This  is  doubtless  owing,  in  some  degree,  to  a 
certain  obscurity  in  the  mode  of  explanation,  and  still  more 
to  the  fact  that  the  writers,  having  had  recourse  only  to  direct 


152 


ANIMAL  MECHANISM. 


observation  in  order  to  analyse  the  paces  of  the  horse,  have 
not  been  able  to  give  all  the  details.  We  trust  that  we  shall 
be  more  fortunate  in  our  treatment  of  the  subject ;  but  we  are 
assured,  at  least,  of  the  perfect  exactitude  of  the  data  fur- 
nished by  the  apparatus  which  we  have  used. 

Colonel  Duhousset  has  been  kind  enough  to  offer  us  his 
assistance  in  representing  the  horse  in  its  various  paces ;  it  is 
to  his  skilful  pencil  that  we  owe  the  figures  represented  in  this 
chapter,  which  are  the  faithful  translation  of  the  notation 
which  accompanies  them.  We  are  also  indebted  to  Mons. 
Duhousset  for  some  documents  relating  to  the  representation 
of  the  paces. 

The  knowledge  of  the  pistes— that  is  to  say,  the  impressions 
which  the  feet  of  the  horse  leave  on  the  ground — is  of  great 
importance  ;  they  enable  an  experienced  eye  to  recognise  the 
pace  of  the  animal  which  has  marked  them. 

These  pistes  are  of  extreme  value  to  the  artist;  they 
alone  can  represent  to  him  the  limbs  as  they  strike  the  ground, 
with  the  true  distances  which  they  ought  to  preserve  from 
each  other  according  to  the  size  of  the  horse  and  the  speed  of 
the  pace.  We  refer  the  reader  to  the  works  of  Vincent  and 
Goiffon,  of  Baron  Curnieu,  of  Colin,  &c,  on  this  subject,  con- 
tenting ourselves  with  giving  merely,  from  these  writers,  the 
piste  which  characterises  each  pace. 

The  first  series  of  experiments,  the  results  of  which  we  are 
about  to  analyse,  were  made  in  the  riding  school  of  Mons. 
Pellier,  Jils.  The  horses  were  furnished,  on  each  foot,  with 
an  instrument  for  determining  pressures,  similar  to  that  which 
is  represented  in  fig.  42.  We  shall  first  discuss  the  experi- 
ments on  the  trot ;  the  tracings  which  they  give  are  easy  to 
be  understood  ;  the  study  of  these  will  serve  as  a  preparation 
for  the  more  complicated  analysis  of  the  other  paces. 

OF  THE  TROT. 

Experiments  on  the  trot. — An  old  and  very  quiet  horse  fur- 
nished the  tracing  represented  in  fig.  45.  In  this  plate  are 
shown  at  the  same  time  the  tracings  of  the  pressures  of  the 
four  feet  with  their  notations,  and  on  the  other  side,  the  re- 
actions produced  on  the  horse  by  this  kind  of  pace. 


ON  THE  TROT. 


153 


154 


ANIMAL  MECHANISM. 


animal,  which  are  given  by  the  line  R  A  (anterior  re-actions), 
and  from  the  croup  for  the  hinder  part,  which  correspond 
with  the  line  R  P  (posterior  re-actions). 

Below  are  given  the  curves  of  pressure  of  the  four  feet ; 
they  are  drawn  at  two  different  levels ;  above  are  the  curves 
of  the  anterior,  below  those  of  the  posterior  limbs.  In  each 
of  these  series  the  curves  of  the  left  foot  are  drawn  with 
dotted  lines,  those  of  the  right  with  full  lines.  Whether 
dotted  or  full,  these  lines  have  been  made  thicker  for  the 
fore-limbs  than  for  the  hinder  ones ;  this  difference,  though 
of  little  use  in  curves  as  simple  as  those  of  the  trot,  will 
serve  to  render  the  more  complicated  tracings  much  more 
intelligible. 

The  moment  when  the  curve  begins  its  rise,  represents  the 
commencement  of  the  pressure  of  the  foot  on  the  ground. 
The  instant  when  the  curve  descends  again  gives  the  signal 
of  the  rise  of  the  foot.*  It  is  seen  from  these  tracings 
that  the  feet  A  G  and  P  D,  left  fore-foot  and  right  hind-foot, 
strike  the  ground  at  the  same  time.  The  simultaneous  lower- 
ing of  the  curves  of  the  two  feet  shows  that  they  also  rise  from 
the  ground  simultaneously.  Under  these  curves  is  the  nota- 
tion which  represents  the  pressure  of  the  left  diagonal  biped.f 

The  second  impact  is  given  by  the  feet  A  D  and  P  G  (right 
diagonal  biped),  and  so  on  through  all  the  length  of  the 
tracing. 

This  experiment  confirms  the  correctness  of  the  standard 
theory  of  the  trot,  and  at  the  same  time  affords  additional 
information  on  some  points.  Thus,  all  writers  agree  in 
choosing,  as  the  type  of  the  free  trot,  the  pace  in  which  all  the 
four  feet  give  but  two  strokes,  and  in  which  the  ground  is 
struck  in  turn  by  the  two  diagonal  bipeds.    It  is  admitted 

*  The  duration  of  the  pressure  ought  to  be  marked  by  a  horizontal  line, 
but  we  have  made  the  tube  somewhat  narrow  in  order  to  lessen  the  force 
of  the  shocks  given  to  the  registering  lever ;  the  narrowing  of  the  tube 
has  slightly  affected  the  curve,  which,  however,  produces  no  inconvenience 
in  studying  the  rhythms. 

t  Each  diagonal  biped  is  named  after  the  anterior  foot  of  which  it  forms 
a  part ;  the  left  diagonal  biped  means,  therefore,  left  fore  foot,  right  hind 
foot 


ON  THE  TROT. 


155 


also  that  the  trot  is  a  high  pace,  and  that,  in  the  interval 
between  two  successive  strokes,  the  animal  is  for  an  instant 
raised  above  the  ground. 

But  we  find  disagreement  when  we  come  to  estimate  the 
duration  of  this  suspension.  Thus,  according  to  Bouley,  it  is 
very  short  in  proportion  to  the  duration  of  the  pressure  ; 
whilst  Raabe  thinks,  on  the  contrary,  that  the  pressure  is 
very  short,  so  that  the  animal  is  a  longer  time  in  the  air  than 
on  the  ground. 

In  the  notation  of  the  tracing  (fig.  45),  it  is  seen  that  the 
pressures  are  twice  as  long  as  the  periods  during  which  the 
body  is  suspended  above  the  ground.  This  experiment,  there- 
fore, would  confirm  the  opinion  of  Bouley  in  opposition  to 
that  of  Raabe;  but  it  appears  to  us  that  there  is  a  great 
variety  in  the  relative  duration  of  the  pressures,  and  of  the 
periods  of  suspension  above  the  ground  during  the  trot. 
Thus,  certain  horses  running  in  harness  have  furnished 
tracings  in  which  the  phase  of  suspension  was  scarcely 
visible ;  so  that  this  form  of  trot  resembled  the  low  paces, 
only  preserving  that  characteristic  of  the  free  type  which 
arises  from  the  perfect  synchronism  of  the  diagonal  strokes  of 
the  feet.  We  have  not  yet  been  able  to  stud}'  the  movements 
of  rapid  trotters ;  in  these  perhaps  we  should  see,  in  an 
inverse  ratio,  the  time  of  suspension  increase  over  that  of  the 
duration  of  pressures. 

If  we  seek  to  ascertain  the  correspondence  between  the 
re- actions  (R  A  and  R  P)  and  the  movements  of  the  limbs,  we 
see  that  the  moment  when  the  body  of  the  animal  is  at  the 
lowest  part  of  its  vertical  oscillation  coincides  precisely  with 
that  at  which  its  feet  touch  the  ground.  The  time  of  suspen- 
sion does  not  depend  on  the  fact  that  the  body  of  the  horse  is 
projected  into  the  air,  but  that  all  four  legs  are  bent  during 
this  short  period.  The  maximum  height  of  the  suspension  of 
the  body  corresponds,  on  the  contrary,  with  the  end  of  the 
pressure  of  the  limbs  on  the  ground.  It  seems,  according  to 
the  tracings,  that  the  elevation  of  the  body  does  not  com- 
mence till  after  each  double  impact,  and  that  it  continues 
during  the  whole  time  of  the  pressure. 

It  is  also  seen,  in  the  same  figure,  that  the  re-actions  of  the 


156 


ANIMAL  MECHANISM. 


fore-limbs  are  much  more  considerable  than  those  of  the 
hinder  ones.  This  fact  appears  to  us  to  be  constant  j  and  the 
inequality  of  the  re -actions  is  still  more  marked  in  the  walk- 
ing pace,  because  the  apparatus  placed  on  the  withers  almost 
always  gives  appreciable  re-actions,  while  that  on  the  croup 
gives  scarcely  any. 

Of  the  irregular  trot  (trot  decomu). — We  call  that  a  free 
trot  which  gives  two  distinct  sounds  to  the  ear  for  each  pace, 
and  we  name  that  irregular,  each  sound  of  which  is  in  a  cer- 
tain degree  divided  by  the  want  of  synchronism  in  the  strokes 
of  each  diagonal  biped.  The  irregular  trot  has  been  met 
with  in  many  of  our  experiments.  Occasionally  this  pace  was 
continued,  and  then  the  want  of  synchronism  existed  some  - 
times in  the  impacts  of  the  two  diagonal  bipeds,  and  some- 
times in  one  pair  only ;  at  other  times,  on  the  contrary,  the 
trot  was  irregular  only  for  an  instant,  at  the  moment  of  the 
passage  from  one  kind  of  pace  to  another.  In  all  the  experi- 
ments which  we  have  hitherto  made,  the  want  of  synchronism 
depended  on  the  hinder  limb  being  behind  the  anterior  limb 
which  corresponded  diagonally  with  it. 

Fig.  46  represents  the  notation  of  an  irregular  trot,  in 
which  the  diagonal  impacts  leave  between  them  an  appre- 
ciable interval  of  time.  We  can  recognise  this  by  the 
obliquity  of  the  dotted  line  which  unites  with  each  other  the 
impacts  of  the  two  diagonal  bipeds. 


Fig.  46.— Notation  of  the  irregular  trot. 


The  piste  of  the  trot  is  represented  in  fig.  47,  according  to 
Vincent  and  Goiffon.  All  the  prints  are  double,  for  the 
hinder-foot  always  comes  up  to  take  the  place  of  the  fore-foot 
on  the  same  side. 

In  fig.  47  we  have  rendered  this  superposition  imperfect 


ON  THE  TROT. 


157 


in  order  to  avoid  confusion ;  for  the  same  purpose,  we  have 
represented  the  prints  of  the  fore-feet  by  dotted  lines,  those  of 
the  hind-feet  by  full  lines.  In  the  trot,  the  prints  of  the  left 
f  ;et  alternate  perfectly  with,  those  of  the  right  feet. 


___„____— ----- 

Fig.  47. — Piste  of  the  trot  according  to  Vincent  and  Goiffon. 


According  to  the  speed  of  the  trot,  and  the  size  of  the 
horse,  the  piste  varies  much  with  respect  to  the  space  which 
separates  the  prints  on  the  same  side 


Fio.  48. — Horse  trotting  wuh  alow  kind  of  pace.  The  instant  corresponding 
with  the  attitude  represented  in  this  figure,  is  marked  with  a  white  dot 
ou  the  notation. 


In  the  representation  of  the  trotting  horse  we  must  dis- 
tinguish the  different  forms  of  this  pace. 

The  low  and  short  trot  is  represented  in  fig.  48.  We  usually 


158  ANIMAL  MECHANISM. 

make  our  observations  at  the  start  of  the  animal,  or  at  the 
moment  when  he  passes  from  the  walking  pace  to  the  trot. 
The  diagonal  impacts  succeed  each  other  without  interval,  as 
is  seen  in  the  notation  placed  below  the  figure.  The  animal 
has  been  depicted  from  the  notation. 

The  instant  which  the  artist  has  chosen  is  that  which  is 
marked  in  the  notation  by  a  white  dot.  At  this  moment,  as 
the  superposition  indicates,  the  left  fore-foot  is  at  the  end  of 
its  pressure  ;  the  right  fore-foot  is  about  to  reach  the  ground ; 
the  right  hind-foot  is  finishing  its  pressure ;  the  left  hind-foot 
is  about  to  fall.  The  inclination  of  the  limbs  is  that  which 
corresponds  with  each  of  the  phases  of  the  pressures  and  the 
rise  of  the  feet.  The  distance  separating  the  feet  is  that 
which  is  indicated  by  the  prints  on  the  ground.  Thus,  in 
fig.  48,  it  is  seen  that  the  trot  is  shortened,  for  the  hind-foot. 


Fig.  49.— Horse  at  full  trot.    The  dot  placed  in  the  notation  corresponds 

with  'he  attitude  represented. 


ON  THE  WALKING  PACE. 


159 


on  the  point  of  striking  the  ground,  will  not  reach  the  place 
of  the  fore-foot  on  the  same  side. 

The  elevated  and  lengthened  trot  is  represented  in  fig.  49, 
which  has  already  served  to  show  the  rider  and  his  horse 
furnished  with  the  instruments  for  the  purpose  of  forming 
tracings  of  the  various  paces.  The  animal  is  depicted  at  the 
instant  which,  in  the  notation,  is  represented  by  a  dot ;  that 
is  to  say,  during  the  time  of  suspension,  at  the  moment  when 
the  left  diagonal  biped  has  just  risen  and  the  right  diagonal 
biped  is  about  to  descend. 

OF   THE   WALKING  PACE. 

Experiments  on  the  walking  pace. — The  explanations  into 
wnich  we  have  entered  in  order  to  analyse  the  tracings  of  a 
trot,  will  facilitate  the  interpretation  of  that  of  the  walking 
pace,  represented  in  fig.  50.  These  tracings  have  been  obtained 
from  the  same  horse  as  the  preceding  ones. 

If  we  let  fall  a  perpendicular  from  the  points  at  which  the 
curves  commence,  we  shall  have  the  position  of  the  successive 
impacts  of  the  four  legs.  On  account  of  the  thickness  of  the 
style  employed  to  trace  these  curves,  the  foot  corresponding 
with  each  of  them  is  easily  recognised,  therefore  we  can 
mark  on  each  of  these  perpendicular  lines  the  initial  letters 
of  the  foot  which  at  this  moment  reaches  the  ground.  The 
order  of  succession  of  impacts  is  represented  by  the  letters 
A  D,  P  G,  A  G,  P  D  ;  that  is  to  say,  right  fore-foot,  left  hind- 
foot,  left  forefoot,  right  hind-foot,  which  is  the  succession 
admitted  by  writers  on  the  subject. 

There  remains  to  be  determined  the  greater  or  less  ropru- 
larity  in  the  succession  of  these  impacts,  and  the  relative 
extent  of  the  intervals  which  separate  them.  For  this  purpose 
it  is  sufficient  to  construct  the  notation  of  the  rhythm  of  the 
pressure  of  each  foot  according  to  the  registered  curves. 
This  notation  for  fig.  50  shows  that  the  interval  which  sepa- 
rates the  impacts  is  always  the  same,  and,  consequently,  that 
the  horse  rests  during  the  same  time  on  the  lateral  as  on  the 
diagonal  bipeds.    But  this  is  not  always  the  case. 

That  we  may  render  the  successive  positions  of  the  centre 
of  gravity  easily  understood,  we  will  explain  in  few  words  the 


OF  THE  WALKING  PACE. 


1G1 


footfalls,  beginning  with  that  of  the  right  fore-foot,  which  is 
marked  No.  1,  we  shall  divide  the  figures  into  successive  por- 
tions, in  which  will  be  found  the  impacts,  sometimes  of  two 
legs  on  the  same  side  (lateral  biped),  at  others,  of  two  placed 
diagonally  (diagonal  biped).  Thus,  from  1  to  2,  the  horse 
will  rest  on  the  right  lateral  biped  ;  from  2  to  3,  on  the  right 
diagonal  biped  (that  is  to  say,  on  that  in  which  the  right  foot 
comes  first) ;  from  3  to  4,  on  the  left  lateral  biped ;  from  4 
to  5,  on  the  left  diagonal  biped  ;  again,  from  5  to  6,  the  horse 
would  find  himself,  as  at  the  beginning,  on  the  right  lateral 
biped. 

This  experiment  has  reference  entirely  to  the  standard 
theory  of  the  pace  (see  No.  5  of  the  synoptical  table),  but 
some  horses  walk  in  a  manner  somewhat  different. 

Fig.  51  is  the  notation  of  the  walking  pace  of  a  horse 
which  rested  longer  on  the  lateral  than  on  the  diagonal 
pressures. 

Sometimes  the  contrary  is  observed  ;  in  the  transitions 
from  the  walk  to  the  trot,  for  instance,  we  have  found  the 
duration  of  the  diagonal  pressures  predominate. 

This  study,  in  order  to  be  complete,  ought  to  have  been 
carried  on  under  more  favourable  conditions  than  those  which 
we  have  hitherto  been  able  to  meet  with.  It  would  be 
desirable  to  obtain  many  horses  belonging  to  different  breeds ; 
to  study  their  movements  when  led  by  the  hand,  mounted,  or 
harnessed  ;  to  vary  the  load  which  they  carry  or  draw ;  to 
experiment  on  level  or  sloping  ground,  &c.  Ail  this  can  only 
be  effected  by  men  especially  interested  in  these  inquiries,  and 
placed  in  favourable  circumstances  to  undertake  them. 

While  making  observations  on  draught  horses,  it  has 
seemed  to  us  that  when  the  animal  strives  to  re-act  against 
the  weight  of  the  carriage  pressing  upon  him,  he  may  have 
three,  feet  on  the  ground  at  once.  This  Borelli  considered 
to  be  the  normal  walking  pace;  we  have  just  seen,  on  the 
contrary,  that  in  the  natural  walking  pace  there  are  never 
more  than  two  feet  on  the  ground  at  a  time. 

As  to  the  re-actions  during  the  walking  pace,  they  are  not 
represented  in  fig.  50.  We  have  ascertained  generally  that 
the  re-actions  of  the  fore-limbs  are  the  only  ones  of  any  iui- 
16  >  . 


162 


ANIMAL  MECHANISM. 


portance  ;  we  are  led  to  suppose,  by  the  extremely  slight  re- 
actions of  the  hinder  parts,  that  their  action  consists  chiefly 
in  a  forward  propulsion,  but  with  very  slight  impulsion  of 
the  body  in  an  upward  direction.  This  agrees  with  the  theory 
somewhat  generally  admitted,  by  which  the  fore-legs  would 
have  little  to  do  in  the  normal  pace  except  to  support  alter- 
nately the  fore  part  of  the  body,  while  to  the  hind  limbs 
would  belong  the  propulsive  action  and  the  tractive  force 
developed  by  the  animal. 

The  piste  of  the  walking  pace,  according  to  Vincent  and 
GoifTon,  is  analogous  with  that  of  the  trot,  except  that  it  pre- 
sents a  shorter  interval  between  the  successive  footprints  on 
the  same  side. 


Fig.  52.— Piste  of  the  walking  pace,  after  Vincent  and  Goiffon. 

In  the  ordinary  walk,  this  distance  would  be  equal  to  the 
height  of  the  horse,  measured  at  the  withers.  As  in  the  trot, 
the  prints  are  covered  at  each  pace ;  those  of  the  right  foot 
alternate  perfectly  with  those  of  the  left.  This  character  of 
the  piste  of  the  walking  pace  is,  however,  observed  only  under 


■ 

O 

.3  D 

Fig.  53.— Piste  of  the  amble,  after  Vincent  and  Goiffon  :  it  differs  from  that 
of  the  walking  pace,  only  by  the  non-superposition  of  the  footprints  on 
the  same  side.  The  hind  foot  is  placed  on  the  ground  beyond  the  im- 
pression of  the  fore  foot. 


certain  conditions  of  speed,  and  on  level  ground.  On  rising 
ground  the  prints  of  the  hind-feet  are  usually  behind  those  of 
the  fore-feet ;  in  a  descent,  on  the  contrary,  they  may  possibly 
pass  beyond  them,  which  would  give  the  piste  of  the  walk 
some  resemblance  to  that  of  the  amble. 


OF  THE  WALKING  PACE. 


163 


Representation  of  a  pacing  horse.  The  representation  of  a 
horse  at  the  walking-  puce  has  been  given  by  Mons.  Duhousset 
in  tig.  54.  The  instant  chosen  is  marked  in  the  notation  by 
a  dot.  We  shall  not  give  an  enumeration  of  the  positions  of 
the  limbs  of  the  animal  as  shown  in  the  notation,  as  we  have 
already  done  so  in  the  representation  of  the  trot. 


Fig.  54.  —Representation  of  the  horse  at  a  walking  pace. 


164 


ANIMAL  MECHANISM. 


CHAPTER  VI. 

EXPERIMENTS  ON  THE  PACES  OF  THE  HORSE. 

(Continued.) 

Experiments  on  the  gallop  —  Notation  of  the  gallop— Re-actions — Bases  of 

support — Pistes  of  the  gallop — Representation  of  a  galloping  horse  in 

the  various  times  of  this  pace. 
Transitions,  or  passage,  from  one  step  to  the  other — Analysis  of  the  paces 

by  means  of  the  notation   rule — Synthetic   reproduction  of  the 

different  paces  of  the  horse. 

OF  THE  GALLOP. 

Several  different  paces,  the  common  character  of  which  is 
that  irregular  impacts  return  at  regular  intervals,  are  compre- 
hended under  this  name.  Most  of  the  writers  distinguish 
three  kinds  of  gallop  by  the  rhythm  of  the  impacts,  and 
name  them,  according  to  this  rhythm,  gallop  in  two,  three, 
and  four  time.  The  most  ordinary  kind  is  the  gallop  in  three- 
time  ;  this  we  shall  study  in  the  first  place. 

Experiments  on  the  gallop.  Fig.  55  has  been  obtained  from 
a  horse  which  galloped  in  three-time.  At  first  sight,  the 
notation  of  this  pace  reminds  us  of  that  which  we  have 
represented  when  speaking  of  human  gallop  (fig.  36,  p.  134), 
a  pace  used  by  children  when  "  playing  at  horses."  It 
appears  that  the  notation  of  the  horse's  gallop  has  been 
obtained  by  placing  one  over  another  two  of  these  notations 
of  the  biped  gallop ;  so  that,  in  fact,  the  comparison  used  by 
Dupes  is  perfectly  just,  even  when  it  is  applied  to  the  gallop. 

Analysis  of  the  tracing.  At  the  commencement  of  the  figure, 
the  animal  is  suspended  above  the  ground ;  then  comes  the 
impact  P  G,  which  announces  that  the  left  hind-foot  touches 
the  ground.  This  is  the  foot  diagonally  opposed  to  that  which 
the  horse  places  forward  in  the  gallop,  and  whose  impact  A  D 
will  be  produced  the  last.  Between  these  two  impacts,  and 
distinctly  in  the  middle  of  the  interval  which  separates  them, 
comes  the  simultaneous  impact  of  the  two  feet  forming  the 


166 


ANIMAL  MECHANISM. 


In  this  series  of  movements  the  ear  has,  therefore,  dis- 
tinguished three  sounds,  at  nearly  equal  intervals.  The  first 
sound  is  produced  by  a  hinder  foot,  the  second  by  a  diagonal 
biped,  the  third  by  a  fore-foot.  Between  the  single  impact  of 
the  fore-foot,  which  constitutes  the  third  sound,  and  the  first 
beat  of  the  pace  which  follows,  reigns  a  silence  whose  dura- 
tion is  exactly  equal  to  that  of  the  three  impacts  taken 
together ;  then  the  series  of  movements  recommences. 

By  the  inspection  of  the  curves,  we  see  that  the  pressure 
of  the  feet  on  the  ground  must  be  more  energetic  in  the 
gallop  than  in  the  other  paces  already  represented,  for  the 
height  of  the  curves  is  evidently  greater  than  for  the  trot, 
and  especially  so  as  compared  with  the  walk.  In  fact,  the 
animal  must  not  only  support  the  weight  of  its  body,  but  give 
it  violent  forward  impulses.  The  greatest  energy  seems  to 
belong  to  the  first  impact.  At  this  moment,  the  body,  raised 
for  an  instant  from  the  ground,  falls  again,  and  one  leg 
alone  sustains  this  shock. 


■113  1  21  3  I     1  |0 


Fig.  56.— Gallop  in  three-time.  (A)  indication  of  three-time.  B.  indication 
of  the  number  of  feet  which  form  the  support  of  the  body  at  each  instant 
of  the  gallop  in  three- time. 


If  we  wish  to  take  account  of  the  successive  pressures  which 
sustain  the  body  during  each  of  the  steps  in  the  gallop,  we 
have  only  to  divide  the  duration  of  this  pace  into  successive 
instants  in  which  the  body  is  sometimes  supported  on  one  or 
on  several  feet,  and  sometimes  suspended.  The  notation  (fig. 
56)  allows  us  to  follow  in  (A)  the  succession  of  impacts,  and 
shows  in  (B)  the  succession  of  the  limbs  which  cause  these 
pressures  on  the  ground. 

If  we  wish  to  ascertain  what  are  the  re-actions  produced  at 
the  withers,  we  see  them  represented  in  fig.  55  (upper  line  R). 
We  find  an  undulatory  elevation,  which  lasts  all  the  time 


OF  THE  GALLOP. 


167 


that  the  animal  touches  the  ground;  in  this  elevation  are 
recognised  the  effects  of  the  three  impacts,  which  give  it  a 
triple  undulation.  The  minimum  elevation  of  the  curve  cor- 
responds, as  in  the  trot,  with  the  moment  when  the  feet  do 
not  touch  the  ground.  Therefore,  it  is  not  a  projection  of  the 
body  into  the  air  which  constitutes  the  time  of  suspension  in 
the  gallop.  Lastly,  by  comparing  the  re-actions  of  the  gallop 
with  those  of  the  trot  (fig.  45),  we  see  that  in  the  gallop  the 
rise  and  fall  of  the  body  are  effected  in  a  less  sudden  manner. 
These  re-actions  are,  therefore,  less  jarring  to  the  rider, 
though  they  may,  in  fact,  present  a  greater  amplitude. 

Piste  of  the  gallop  in  three-time. — According  to  Curnieu,  this 
piste  is  the  following : — 


^3 

D 

3              D  D 

D 

D  S3 

D  S3 

D 

Fig.  57. — Piste  of  the  short  gallop  in  three-time.  The  hinder  feet,  whose 
prints  have  the  fiinn  of  an  U,  reach  the  ground  in  front  of  the  prints  of 
the  fore  feet.  The  latter  have  been  represented  by  a  form  somewhat  like 
an  O. 


The  piste  of  the  gallop  varies  according  to  the  speed.  In 
the  short  gallop  of  the  riding  school,  the  hind-feet  leave  their 
prints  behind  those  of  the  fore-feet ;  in  the  rapid  gallop,  on 
the  contrary,  they  come  in  front  of  the  prints  of  the  fore-feet. 
A  horse  which,  in  the  pace  of  the  riding  school,  gallops 
almost  entirely  within  his  own  length,  will,  when  started  at 
full  gallop,  cover  an  enormous  space.  According  to  Curnieu, 
the  famous  Eclipse  covered  22  English  feet.  The  following 
is  the  piste  which  this  very  rapid  pace  leaves  on  the  ground  : — 


D 

"D 

D 

« 

D 

"Z3 

D 

D 

P 

O 

FiO.  58.— Piste  of  Eclipte's  gallop,  from  Curnieu.    The  prints  of  the  hind- 
feet  are  very  far  before  those  of  the  fore-feet. 


Representation  of  a  horse  galloping. — For  this  representation 
we  will  give  tluee  attitudes,  differing  much  from  each  other, 


168  ANIMAL  MECHANISM. 


and  corresponding  nearly  with  the  three  kinds  of  time  found 
in  this  pace. 


Fig.  59.— Horse  galloping  in  the  first  time  fright  foot  advancing),  the  hind  left 
foot  only  on  the  ground.  The  white  dot,  in  the  notation,  corresponds 
with  the  instant  at  which  the  horse  is  represented. 


In  the  first  time,  fig.  59,  the  left  hind-foot,  on  which  the 
horse  has  just  descended,  alone  rests  on  the  ground. 

In  the  second  time,  fig.  60,  the  left  diagonal  biped  has  just 
finished  its  impact,  the  right  fore-foot  is  about  to  reach  the 
ground,  the  left  hind-foot  has  just  risen. 

The  third  time  of  the  gallop,  fig.  61,  has  been  drawn  as 
well  as  the  others  by  Mons.  Duhousset  according  to  the  nota- 
tion; the  moment  chosen  is  that  in  which  the  right  foot 
alone  rests  on  the  ground,  and  is  about  to  rise  in  its  turn. 


370 


ANIMAL  MECHANISM. 


The  figure  which  represents  it  is  rather  strange  ;  the  eye  is 
but  little  accustomed  to  see  this  time  of  the  gallop,  which  is 
doubtless  very  rare.  When  considering  this  ungraceful  figure, 
we  are  tempted  to  say  with  De  Curnieu,  "  the  province  of 
painting  is  what  one  sees,  and  not  what  really  exists." 

The  gallop  in  four-time  differs  from  that  which  has  just 
been  described  only  in  this  point,  that  the  impacts  of  the 
diagonal  biped,  which  constitute  the  .second  time,  are  disunited 
and  give  distinct  sounds  ;  we  see  an  example  of  this  in  fig.  62. 


4  TEMPS.  A 

B  ■ 

i 

3  |2|  1 

0 

Fig.  62. — Notation  of  the  gallop  in  four- time.  (A)  determination  of  each 
of  the  successive  times.  (B)  determination  of  the  number  of  feet  which 
support  the  body  at  each  instant. 


According  to  this  notation,  the  body,  at  first  suspended,  is 
borne  successively  on  one  foot,  on  three,  on  two,  on  three,  and 
on  one,  after  which  a  new  suspension  recommences. 

Of  the  full  gallop. — This  very  rapid  pace  could  not  be 
studied  by  means  of  the  apparatus  which  we  have  employed 
hitherto.  It  was  necessary  to  construct  a  special  registering 
instrument,  and  new  experimental  apparatus. 

To  leave  the  two  hands  of  the  rider  free,  the  registering 
instrument  was  enclosed  in  a  flat  box,  attached  to  the  back  of 
the  horseman  by  straps  like  the  knapsack  of  the  soldier.  We 
shall  not  attempt  the  detailed  description  of  this  instrument, 
which  carried  five  levers,  tracing  on  smoked  glass  the  curves 
of  the  action  of  the  four  legs,  and  the  reaction  of  the  withers. 
The  violence  of  the  impacts  on  the  ground  is  such  that  they 
would  instantly  have  broken  the  apparatus  before  employed. 
We  have  substituted  for  this  a  copper  tube,  in  which  moves  a 
leaden  piston,  suspended  between  two  spiral  springs.  The 
shocks  given  to  this  piston  at  each  footfall,  produce  an  effect 
like  that  of  an  air-pump  acting  on  the  registers.  A  ball  of 
india-rubber,  which  can  be  pressed  between  the  teeth,  sets  the 


OF  THE  GALLOP. 


171 


register  going,  and  allows  the  tracing  to  be  taken  at  a  suitable 
time.' 

Through  the  kindness  of  Mons.  H.  Deiamarre,  who  placed 
at  our  disposal  his  stables  at  Chantilly,  we  have  been  able  to 
procure  tracings  of  the  full  gallop,  of  which  the  following  is 
the  notation : — 


Fig.  63.— Notation  of  full  gallop;  re-actions  of  this  pace. 

It  is  seen  that  this  pace  is,  in  reality,  a  gallop  in  four-time. 
The  impacts  of  the  hinder  limbs,  however,  follow  each  other 
at  such  short  intervals,  that  the  ear  can  only  distinguish  one 
of  them ;  but  those  of  the  fore-legs  are  noticeably  more  dis- 
sociated, and  can  be  heard  separately.  Another  character  of 
the  full  gallop  is,  that  the  longest  period  of  silence  takes 
place  during  the  pressure  of  the  hinder  limbs.  The  time  of 
suspension  appears  to  be  extremely  short. 

To  get  the  best  possible  results  from  these  experiments,  it 
would  be  necessary  to  repeat  them  on  a  great  number  of 
horses,  and  to  ascertain  whether  there  may  not  be  some  rela- 
tion between  the  rhythm  of  the  impacts  and  the  other 
characters  of  the  pace.  We  must  leave  this  task  to  those 
who  especially  addict  themselves  to  the  study  of  the  horse. 

Lastly,  let  us  add,  that  the  re-actions,  in  full  gallop,  repro- 
duce with  great  exactness  the  rhythm  of  the  impacts.  Thus, 
it  is  observed,  that  at  the  moment  of  the  almost  synchronous 
impacts  of  the  two  hinder  limbs,  there  is  a  sharp  and  pro- 
longed re-action,  after  which  two  less  sudden  re-actions  take 
place,  each  of  which  corresponds  with  the  impact  of  one  of 
the  fore-legs. 

The  line  placed  above  fig.  63  is  the  tracing  of  the  re-actions 


ANIMAL  MECHANISM. 


of  the  withers.  This  curve,  being  placed  above  the  notation, 
enables  us,  by  the  superposition  of  its  various  elements,  to 
notice  with  which  impact  of  the  limbs  each  re-action  cor- 
responds. 

OF   THE   TRANSITIONS   BETWEEN   THE   DIFFERENT  KINDS 
OF  PACES. 

An  observer  finds  great  difficulty  in  ascertaining  how  one 
kind  of  pace  passes  into  another.  The  graphic  method  fur- 
nishes a  very  easy  means  of  following  these  transitions ;  this 
will  perhaps  be  not  one  of  the  least  advantages  of  the  employ- 
ment of  this  method  of  studying  the  paces  of  the  horse. 

In  order  thoroughly  to  understand  what  takes  place  in  these 
transitions,  we  must  refer  again  to  the  comparison  made  by 
Duges,  and  represent  to  ourselves  two  persons  walking,  and 
following  each  other's  footsteps,  both  in  the  trot  and  the 
gallop.  In  these  continued  paces,  these  two  persons  present 
a  constant  rhythm  in  the  relation  of  their  movements  ;  while, 
in  the  transitions,  the  foremost  or  hindermost  person,  as  the 
case  may  be,  quickens  or  moderates  his  movements  so  as  to 
change  the  rhythm  of  the  footfalls.  Some  examples  will 
render  this  more  evident. 

The  principal  transitions  are  represented  in  page  174. 

Fig.  64  is  the  notation  of  the  transition  from  the  walking 
face  to  the  trot.  The  dominant  character  of  this  change,  inde- 
pendently of  the  increase  of  rapidity,  consists  in  the  hinder 
impacts  gaining  upon  those  of  the  fore-limbs ;  so  that  the 
impact  of  the  left  hind-foot,  P  G,  for  instance,  which,  during 
the  walking  pace,  took  place  exactly  in  the  middle  of  the 
duration  of  the  pressure  of  the  right  fore-foot,  A  D,  gradually 
advances  till  it  coincides  with  the  commencement  of  the 
pressure  A  D,  and  with  the  impact  also,  at  which  time  the 
trot  is  established. 

Fig.  65  indicates,  on  the  contrary,  the  transition  from  the 
trot  to  the  walk.  We  see  here,  in  an  inverse  manner,  the 
diagonal  impacts,  synchronous  at  first,  become  more  and  more 
separated.  A  dotted  line,  which  unites  the  left  diagonal 
impacts,  is  vertical  at  the  commencement  of  the  figure  in  the 
part  which  corresponds  with  the  pace  of  the  trot ;  by  degrees 


TRANSITION  OF  PACES. 


173 


this  line  becomes  oblique,  showing  that  the  synchronism  is 
disappearing.  The  direction  of  the  obliquity  of  this  line 
proves  that  the  hinder  limbs  grow  slower  in  their  movements 
in  passing  from  the  trot  to  the  walk. 

In  the  passage  from  the  trot  to  the  galh>p  the  transition  is 
very  curious ;  it  is  represented  by  the  notation,  fig.  66.  We 
6ee,  from  the  very  commencement  of  the  figure,  that  the  trot 
is  somewhat  irregular ;  the  dotted  line  which  unites  the  left 
diagonal  impacts  A  G,  P  D,  is  at  first  rather  oblique,  and  in- 
dicates a  slight  retardation  of  the  hind-foot.  This  obliquity 
constantly  increases,  but  only  for  the  left  diagonal  biped  ;  the 
right  diagonal  biped  A  D,  P  G,  remains  united,  even  after 
the  gallop  is  established.  The  transition  from  the  trot  to  the 
gallop  is  made,  not  only  by  the  retardation  of  the  hind-foot, 
but  by  the  advance  of  the  fore-foot,  so  that  two  of  the  diagonal 
impacts,  which  were  synchronous  in  the  trot,  leave  the  greater 
interval  between  them;  that  which  in  the  ordinary  gallop  con- 
stitutes the  great  silence.  An  opposite  change  produces  the 
transition  from  the  gallop  to  the  trot,  as  is  seen  in  fig.  67.  The 
transition  from  the  gallop  in  four-time  to  that  in  three-time  is 
made  by  an  increasing  anticipation  of  the  impacts  of  the 
hinder  limbs. 

SYNTHETIC   STUDY   OF  THE   PACES   OF   THE  HORSE. 

The  analytical  method  to  which  we  have  hitherto  had 
recourse  in  describing  the  paces  of  the  horse  may  have  left 
many  things  obscure  in  this  delicate  question.  We  hope  to 
clear  them  up  by  recurring  to  the  synthetic  method. 

When  tracing,  at  the  commencement  of  this  study,  the 
synoptical  table  of  the  different  paces,  we  classed  their  nota- 
tions in  a  natural  series,  the  first  term  of  which  is  the  amble, 
and  in  which  the  difference  between  one  step  and  the  next 
consists  in  an  anticipation  of  the  action  of  the  hinder  limbs. 
This  transition  is  just  what  is  observed  in  animals.  A  drome- 
dary, for  instance,  whose  normal  pace  is  the  broken  amble,* 

*  Through  the  kindness  of  Mons.  Geoffrey  St.  Hilaire,  director  of  the 
"  Jardin  d'Acclimatation,"  we  have  been  permitted  to  study  the  paces  of 
different  quadrupeds,  and  especially  those  of  the  large  dromedary  which 
that  garden  possesses. 

17 


TRANSITION  OF  PACES. 


175 


has  given  us  the  whole  series  of  notations,  which,  in  our 
synoptical  table,  separate  No.  2  from  No.  8.  When  urging 
on  the  animal  and  forcing  him  to  trot,  he  first  broke  his  amble 
in  an  exaggerated  manner,  then  he  began  to  walk,  and  after- 
wards commenced  an  irregular  trot,  which  soon  became  a  free 
trot.  We  have  just  seen  that  the  paces  of  the  horse  are  formed 
in  the  same  order  when  the  animal  passes  from  the  walk  to 
the  trot. 

When  a  horse  begins  to  move  more  slowly,  the  change  of 
pace  is  effected  in  an  inverse  manner  ;  the  paces  succeed  each 
other  by  running  up  the  series  represented  in  the  plate. 

The  greater  or  less  anticipation  of  the  action  of  the  hinder 
limbs  is  represented  in  the  plate  by  a  sliding  backward  of  the 
notation  towards  the  left  of  the  figure.  This  fictitious  sliding 
may  become  real  by  using  a  little  instrument,  which  enables 
us  to  understand  and  explain  very  simply  the  formation  of  the 
different  paces.  It  consists  of  a  little  rule,  somewhat  analo- 
gous to  the  sliding  rule  used  in  calculation,  and  which  carries 
the  notations  of  the  four  limbs  on  four  little  slips,  which  can 
glide  side  by  side,  and  be  arranged  in  various  positions. 


Fig.  68.— Notation  rule,  to  represent  the  different  pacea 

Figs.  68  and  69  show  the  arrangement  of  this  little  instru- 
ment. Let  us  imagine  a  rule  made  of  black  wood,  having 
four  narrow  grooves,  in  which  slip  sliding  portions,  alternately 
black  and  white,  or  grey  and  black,  in  order  to  represent  the 
notation  of  the  amble,  as  in  No.  1  of  the  plate.  If  we  push 
towards  the  left  the  two  lowest  slides  simultaneously  (fig.  68), 
we  shall  form,  according  to  the  amount  of  displacement,  one 


176 


ANIMAL  MECHANISM. 


or  other  of  the  notations  in  the  table  of  regular  paces.  A 
scale,  marked  1,  2,  3,  4,  &c,  up  to  which  we  can  bring  the 
mark  representing  the  left  hinder  impact,  allows  us  to  form 
without  hesitation  any  notation  whatever. 

To  form  the  notations  of  the  gallop,  it  is  necessary  to  shift 
the  slides  corresponding  with  the  fore-legs,  so  as  to  make 
them  encroach  on  each  other  as  is  seen  in  notation,  fig.  69. 


Fig.  69.— Notation  rule  forming  the  representation  of  the  gallop  in  three- 
time. 


The  notation  rule  is  thus  used.  When  we  are  sure  that 
the  pace  is  regular,  it  is  sufficient,  for  instance,  to  examine 
the  impacts  of  the  two  right  feet,  in  order  to  construct  the 
whole  notation.  According  as  the  hinder  impact  is  synchro- 
nous with  that  in  front,  or  precedes  it  by  a  quarter,  half, 
three-quarters,  or  the  whole  of  the  duration  of  a  pressure,  we 
place  the  two  lower  slides  in  the  position  which  they  ought  to 
occupy,  and  the  notation  is  thus  simply  constructed ;  it  shows 
the  rhythms  of  the  impacts,  the  duration  of  the  lateral  and 
diagonal  pressures,  &c.  The  construction  of  the  various 
paces  of  the  gallop  is  effected  in  the  same  manner. 

The  artist  who  wishes  to  represent  a  horse  at  any  instant 
of  a  particular  pace,  can  thus  easily  determine  the  correspond- 
ing attitude.  He  forms  on  his  rule  the  notation  of  the  pace 
of  the  horse  which  is  to  be  represented.  Then,  on  the  length 
which  corresponds  with  the  extent  of  a  single  pace  in  this 
notation,  he  erects  a  perpendicular  line  at  any  point.  This 
line  corresponds  with  a  certain  instant  of  the  pace.  Thus,  as 
he  can  trace,  on  the  length  corresponding  with  a  single  pace, 


PACES  OF  THE  HORSE. 


177 


an  indefinite  number  of  perpendicular  lines,  it  follows  that  the 
artist  may  choose  in  the  duration  of  any  pace,  in  any  kind  of 
locomotion,  an  indefinite  number  of  different  attitudes.  Sup- 
pose him  to  have  made  his  choice,  and  that  he  wishes  to 
represent  in  the  kind  of  pace  (fig.  68),  the  instant  which  is 
marked  by  the  vertical  line  7,  the  notation  will  show  him  that 
the  right  fore-foot  has  just  been  placed  upon  the  ground,  that 
the -left  fore-foot  is  therefore  beginning  to  rise,  that  the  right 
hind-foot  is  almost  at  the  end  of  its  pressure  on  the  ground, 
and  that  the  left  hind-foot  is  near  the  end  of  its  rise.  All 
that  is  necessary,  in  order  to  represent  the  animal  exactly,  is 
to  know  the  attitude  of  each  limb  at  the  different  instants  of 
its  rise,  fall,  or  pressure,  which  is  a  comparatively  easy  matter. 
But  the  artist,  guided  by  this  method,  will  thus  inevitably 
avoid  altogether  those  false  attitudes  which  often  cause  repre- 
sentations of  horses  to  be  so  utterly  unnatural. 

FIGURES  ARRANGED   TO   SHOW   THE    PACES    OF    THE  HORSE. 

Mons.  Mathias  Duval  has  undertaken  to  make,  in  order  to 
illustrate  the  locomotion  of  the  horse,  a  series  of  pictures, 
which,  seen  by  means  of  the  zootrope,  represent  the  animal 
as  if  in  motion  in  the  various  kinds  of  paces.  This  ingenious 
physiologist  formed  the  idea  of  reproducing  in  an  animated 
form,  as  it  were,  that  which  notation  has  done  for  the  rhythm 
of  the  movements.  The  following  is  the  arrangement  which 
he  employed.  He  first  drew  a  series  of  figures  of  the  horse 
taken  at  different  instants  of  an  ambling  pace.  Sixteen  suc- 
cessive figures  enabled  him  to  represent  the  series  of  positions 
which  each  limb  successively  assumes  in  a  pace  belonging  to 
this  kind  of  locomotion.  This  band  of  paper,  when  placed 
in  the  instrument,  gives  to  the  eye  the  appearance  of  an 
ambling  horse  in  actual  motion. 

We  have  said  that  all  the  walking  paces  may  be  considered 
as  derived  from  the  amble,  with  a  more  or  less  anticipation  of 
the  action  of  the  hind  limbs.  Mons.  Duval  lias  realised  this 
in  his  pictures  in  the  following  manner.  Each  plate,  on 
which  has  been  drawn  the  series  of  pictures  of  the  ambling 
horse,  is  formed  of  two  sheets  of  paper  placed  the  one  on  the 
other.    The  upper  one  has  in  it  a  number  of  slits  or  openings, 


178 


ANIMAL  MECHANISM. 


bo  that  each  horse  is  drawn  half  on  this  sheet,  and  the  other 
half  on  that  which  is  placed  beneath.  The  hind  quarters, 
for  example,  having  been  drawn  on  the  upper  sheet,  the  fore 
quarters  are  drawn  on  the  under  sheet,  and  are  visible  through 
the  portion  cut  out  of  the  upper  sheet.  Let  us  suppose  that 
we  cause  the  upper  paper  to  slide  as  far  as  the  interval  which 
separates  two  figures  of  the  horse,  we  shall  have  a  series  of 
images  in  which  the  fore  limbs  will  fall  back  a  certain  dis- 
tance towards  the  hind  limbs.  We  shall  thus  represent, 
under  the  form  of  pictures,  what  is  obtained  under  the  form  of 
notation,  by  slipping  the  two  lower  slides  of  the  notation  rule 
one  degree.  And  as  this  displacement  to  the  distance  of  one 
degree  for  each  of  .the  movements  of  the  hinder  limbs  gives 
the  notation  of  the  broken  amble,  we  shall  obtain,  in  the 
figures  thus  drawn,  the  series  of  the  successive  positions  of 
the  paces  of  the  broken  amble.  If  the  paper  be  made  to  slip 
a  greater  number  of  degrees,  we  shall  have  the  series  of  atti- 
tudes of  the  horse  at  his  walking  pace.  A  still  greater  dis- 
placement will  give  the  attitudes  of  the  trot. 

In  all  these  cases,  these  figures,  when  placed  in  the  instru- 
ment, make  the  illusion  complete,  and  show  us  a  horse  which 
ambles,  walks,  or  trots,  as  the  case  may  be.  Then,  if  we 
regulate  the  swiftness  of  the  rotation  given  to  the  instrument, 
we  render  the  movements  which  the  animal  seems  to  execute 
more  or  less  rapid,  which  will  permit  the  inexperienced 
observer  to  follow  the  series  of  positions  of  each  kind  of  pace, 
and  soon  enable  him  to  distinguish  with  the  eye  a  series  of 
movements  in  the  living  animal  which  appear  at  first  sight  to 
be  in  absolute  confusion. 

We  hope  that  these  plates,  though  still  somewhat  defective, 
will  soon  be  sufficiently  perfect  to  be  of  real  use  to  those  who 
are  engaged  in  the  artistic  representation  of  the  horse. 

After  these  studies  of  terrestrial  locomotion,  we  ought  to 
explain  the  mechanism  of  aquatic  locomotion.  Some  recent 
experiments  of  Mons.  Ciotti  have  thrown  great  light  on  the 
propulsive  action  of  the  tails  of  fishes  ;  not  that  they  have 
overthrown  the  theory  held  ever  since  the  time  of  Borelli, 
concerning  the  mechanism  of  swimming,  but  they  have  ap- 
proached tiie  question  in  another  manner,  that  of  the  synthetic 


PACES  OF  THE  HORSE. 


179 


reproduction  of  this  phenomenon.  This  method  will  certainly 
permit  us  to  determine,  with  a  precision  hitherto  unknown, 
both  the  motive  work  and  resistant  work  in  aquatic 
locomotion.  It  will,  therefore,  be  advisable  to  wait  for  the 
results  of  experiments  which  are  now  being1  made,  and 
which  will  be  of  equal  service  both  to  mechanicians  and  to 
physiologists. 


BOOK  THE  THIRD. 

AERIAL  LOCOMOTION. 


CHAPTER  I. 

OF  THE  FLIGHT  OF  INSECTS. 

Frequency  of  the  strokes  of  the  wing  of  insects  during  flight ;  acoustic 
determination  ;  graphic  determination — Influences  which  modify  the 
frequency  of  the  movements  of  the  wing— Synchronism  of  the  action 
of  the  two  wings— Optical  determination  of  the  movements  of  the 
wing;  its  trajectory  ;  changes  in  the  plane  of  the  wing;  direction 
of  the  movement  of  the  wing. 

In  terrestrial  locomotion  we  have  been  able  to  measure  by 
experiment  the  pressure  of  the  feet  on  the  ground,  and  hence 
we  have  deduced  the  intensity  of  the  re-actions  on  the  body 
of  the  animal.  These  two  forces  were  easily  ascertained  by 
direct  measurement.  In  the  problem  which  is  now  to  occupy 
us,  the  conditions  are  very  different.  The  air  gives  a  certain 
resistance  to  the  wings  which  strike  upon  it,  but  it  is  a  resis- 
tance every  instant  yielding,  for  it  is  only  in  proportion  to  the 
rapidity  with  which  it  is  displaced,  that  the  air  resists  the 
impulse  of  the  wing.  When  we  study  the  phenomena  of  flight, 
it  is  therefore  necessary  to  know  the  movement  of  the  wing  in 
all  the  phases  of  its  speed,  in  order  to  estimate  the  resistance 
which  the  air  presents  to  that  organ.  We  will  propound  in 
the  following  order  the  questions  which  must  be  resolved. 

1 .  What  is  the  frequency  of  the  movements  of  the  wing  of 
insects  ? 

2.  What  are  the  successive  positions  which  the  wing  occu- 
pies during  its  complete  revolution  ? 


FLIGHT  OF  INSECTS. 


181 


3.  How  is  the  motive  force  which  sustains  and  transports 
the  body  of  the  animal  developed  ? 

1.  Frequency  of  the  movements  of  the  wing  of  insects. — The 
frequency  of  the  movements  of  the  wing  varies  according  to 
species.  The  ear  perceives  an  acute  sound  during  the  flight 
of  mosquitos  and  certain  flies  ;  there  is  a  graver  sound  during 
the  flight  of  the  bee  and  the  drone  fly ;  still  deeper  in  the 
macroglossse  and  the  sphingidae.  As  to  the  other  lepidoptera, 
they  have,  in  general,  a  silent  flight  on  account  of  the  few 
strokes  which  they  give  with  their  wings. 

Many  naturalists  have  endeavoured  to  determine  the  fre- 
quency of  the  strokes  of  the  wing  by  the  musical  note  pro- 
duced by  the  animal  as  it  flies.  But  in  order  that  this  deter- 
mination should  be  thoroughly  reliable,  it  must  be  clearly 
established  that  the  sound  produced  by  the  wing  depends 
exclusively  on  the  frequency  of  its  movements,  in  the  same 
manner  as  the  sound  of  a  tuning-fork  results  from  the  fre- 
quency of  its  vibrations.  But  opinions  differ  on  this  subject ; 
certain  writers  have  thought  that  during  flight  there  is  a 
movement  of  the  air  through  the  spiracles  of  insects,  and  that  the 
sound  which  is  heard  depends  on  these  alternate  movements. 

Without  giving  our  adherence  to  this  opinion,  which 
seems  to  be  contradicted  by  many  ffjcts,  we  think  that  the 
acoustic  method  is  insufficient  to  furnish  an,  estimate  of  the 
frequency  with  which  the  wing  moves.  The  reason  which 
would  induce  us  not  to  employ  this  method,  is  that  the 
musical  note  produced  by  the  flying  insect  is  varied  by  other 
influences  besides  the  changes  in  the  strokes  of  the  wing. 

When  we  observe  the  buzzing  of  an  insect  flying  with  a 
uniform  rapidity,  we  perceive  that  the  tone  does  not  continue 
constantly  the  same.  As  the  insect  approaches  the  ear,  the 
tone  rises ;  it  sinks  as  it  goes  farther  from  us.  Something  of 
an  analogous  kind  happens  when  we  cause  a  vibrating 
tuning-fork  to  pass  before  the  ear ;  the  note  at  first  becomes 
more  shrill  and  then  more  grave,  and  the  difference  may 
attain  to  a  quarter  or  even  to  half  a  tone.  We  must,  there- 
fore, take  care  that  the  insect  on  which  we  experiment  should 
be  always  at  the  same  distance  from  the  observer.  This  dis- 
turbing phenomenon,  however,  presents  no  real  difficulty  of 


v  182 


ANIMAL  MECHANISM. 


interpretation;  Pisko,  the  German  writer  on  acoustics,  has 
perfectly  explained  it.  There  is  no  doubt  that  the  vibrations 
always  follow  each  other  after  the  same  interval  of  time  ;  when 
a  vibrating  plate  remains  at  the  same  distance  from  the  ear, 
the  vibrations  require  the  same  time  to  reach  us,  and  the 
phenomenon,  uniform  for  the  instrument,  is  uniform  also  for 
our  organ.  On  the  contrary,  if  the  instrument  be  brought 
rapidly  nearer,  the  vibration  which  is  produced  every  instant 
has  less  space  to  traverse  before  it  reaches  the  tympanum ;  it 
thus  approximates  to  that  which  preceded  it,  and  the  sound 
grows  sharper.  If  the  instrument  be  removed  to  a  greater 
distance  the  vibrations  are  more  extended,  and  the  tone  be- 
comes more  grave.  Every  one  has  remarked,  when  travelling 
on  a  railroad,  that  if  a  locomotive  passes  us  while  the  driver 
is  sounding  the  whistle,  the  sharpness  of  the  tone  increases  as 
the  engine  comes  nearer,  and  becomes  graver  when  it  has 
passed  by  us,  and  the  whistle  is  rapidly  carried  to  a  greater 
distance. 

From  these  considerations  we  must  be  convinced  that  it  is 
very  difficult  to  estimate  from  the  musical  tone  produced  by 
a  flying  insect,  the  absolute  frequency  of  the  strokes  of  its 
wings.  This  depends  to  some  extent  on  the  variation  of  the 
tone  thus  produced,  which  passes  at  each  instant  from  grave  to 
sharp,  according  to  the  rapidity  and  the  direction  of  the  flight. 
Besides  this,  it  is  not  easy  to  assign  to  each  wing  the  part 
which  it  plays  in  the  production  of  the  sound.  We  have  also 
to  take  into  consideration  that  the  wing  of  an  insect  may,  by 
brushing  through  the  air  as  it  flies,  be  subjected  to  sonorous 
vibrations  much  more  numerous  than  the  complete  revolutions 
which  it  accomplishes. 

The  graphic  method  furnishes  a  simple  and  precise  solution 
of  the  question ;  it  enables  us  to  ascertain  almost  to  a  single 
beat  the  number  of  movements  made  per  second  by  an  insect's 
win  j?. 

Experiment. — A  sheet  of  paper  blackened  by  the  smoke 
of  a  wax-candle,  is  stretched  upon  a  cylinder.  This  cylinder 
turns  uniformly  on  itself  at  the  rate  of  a  turn  in  a  second 
and  a-half. 

The  insect,  the  frequency  of  the  movement  of  whose  wings 


FLIGHT  OF  INSECTS. 


183 


is  to  be  studied,  is  held  by  the  lower  part  of  the  abdomen,  in 
a  delicate  pair  of  forceps ;  it  is  placed  in  such  a  manner  that 
one  of  its  wings  brushes  against  the  blackened  paper  at  every 
movement.  Each  of  these  contacts  removes  a  portion  of 
the  black  substance  which  covers  the  paper,  and,  as  the 
cylinder  revolves,  new  points  continually  present  themselves 
to  the  wing  of  the  insect.  We  thus  obtain  a  perfectly  regular 
figure,  if  the  insect  be  held  in  a  steadily  fixed  position.  These 
figures,  of  which  we  give  some  examples,  differ  according  as 
the  contact  of  the  wing  with  the  paper  has  been  more  or 
less  extended.  If  the  contact  be  very  slight,  we  obtain  a 
series  of  points  or  short  cross-lines,  as  in  fig.  70. 


Fig.  70. — Showing  the  frequency  of  the  strokes  of  the  winpof  a  drone-fly 
(the  three  upper  lines),  and  of  a  bee  (the  lower  dotted  line*.  Thifouth 
line  is  produced  by  the  vibrations  of  a  chronographs  tuning- ork,  fur- 
nished with  a  style  which  registers  250  double  vibrations  per  second. 

Knowing  that  the  cylinder  revolves  once  in  a  second  and 
a- half,  it  is  easy  to  see  how  many  revolutions  of  the  w  ing 
are  thus  marked  on  the  whole  circumference  of  the  cylinder. 
But  it  is  still  more  convenient  and  accurate  to  make  use  of  a 
chronographic  tuning-fork,  and  to  register,  near  the  figure 
traced  by  the  insect,  the  vibrations  of  the  style  with  which 
the  tuning-fork  is  furnished. 

Fig.  70  shows,  by  the  side  of  the  tracing  made  by  the 
wing  of  a  drone-fly,  that  of  the  vibrations  of  a  tuning  fork, 
which  executes  a  double  oscillation  250  times  in  a  second, 
This  instrument,  enabling  us  to  give  a  definite  value  to  any 
portion  of  the  tracing,  shows  that  the  wing  of  the  drone  per- 
formed from  240  to  250  complete  revolutions  per  second. 


184? 


ANIMAL  MECHANISM. 


Influences  wliich  modify  the  frequency  of  the  movements  of  the 
wing.  —  Since  we  know  the  influence  of  resistance  to  the  rapidity 
of  the  movements  of  animals,  we  may  suppose  that  the  wing 
which  rubs  on  the  cylinder  has  not  its  normal  rate  of  motion, 
and  that  its  revolutions  are  less  numerous  in  proportion  as 
the  friction  is  greater.  Experiment  has  confirmed  this  opinion. 
An  insect  performing  the  movements  of  flight  by  rubbing  its 
wings  rather  strongly  against  the  paper  gave  240  movements 
per  second ;  by  diminishing  more  and  more  the  contacts  of 
the  wing  with  the  cylinder,  we  obtained  still  greater  numbers 
— 282,  305,  and  321.  This  last  number  may  perhaps  ex- 
press with  sufficient  accuracy  the  rapidity  of  the  wing  when 
moving  freely,  for  the  tracing  was  reduced  to  a  series  of 
scarcely-visible  points.  On  the  contrary,  as  the  wing  rubbed 
more  strongly,  the  frequency  of  its  movements  w^as  reduced 
below  240. 

Another  modifying  cause  of  the  frequency  of  movement  in 
the  wing  is  the  amplitude  of  these  movements.  We  must 
compare  this  cause  with  the  preceding,  for  it  is  natural  to 
admit  that  great  movements  meet  with  greater  resistance  in 
the  air  than  smaller  ones. 

When  we  hold  a  fly  or  a  drone  by  the  forceps,  we  see  that 
the  animal  executes  sometimes  strong  movements  of  flight ; 
we  then  hear  a  grave  sound ;  but  occasionally,  when  its  wing 
is  only  slightly  agitated,  we  perceive  only  a  very  shrill  tone. 
That  which  the  ear  reveals  to  us  with  regard  to  the  difference 
in  the  frequency  of  the  strokes  which  the  insect  gives  with  its 
wings,  is  entirely  confirmed  by  the  experiments  which  we 
have  made  graphically. 

Choosing  the  instants  when  the  insect  is  at  its  strongest 
flight,  and  also  when  it  gently  flutters  its  wing,  we  find  that 
the  frequency  varies  within  very  extensive  limits,  nearly  in 
the  proportion  of  one  to  three — the  least  frequency  belonging 
to  the  movements  of  greatest  amplitude. 

The  different  species  of  insects  on  which  we  have  experi- 
mented, presented  also  very  great  variations  in  the  rapidity  of 
the  movements  of  their  wiugs.  We  have  endeavoured  as  far 
as  possible  to  compare  the  different  species  under  similar  con- 
ditions, during  their  swiftest  flight,  and  with  slight  friction 


FLIGHT  OF  INSECTS. 


185 


on  the  cylinder.  The  following  are  the  results  obtained  as 
the  expressions  of  the  number  of  movements  of  the  wing  per 
second  in  each  species  : — 

Common  fly       ....        .  330 

Drone-fly      .        .        ...        .    .  240   I1/ yd 

Bee   190 

Wasp   110 

Humming-bird  moth  (Macroglossa)  .  72 
Dragonfly     .  .        .    .  28 

Butterfly  (Pontia  Rapae)       ...  9 

Synchronism  of  the  action  of  the  two  wings. — By  holding  the 
insect  in  a  suitable  position  we  can  make  both  wings  rub  on 
the  cylinder  at  the  same  time.  It  is  then  seen,  on  the 
tracing,  that  the  two  wings  act  simultaneously,  and  that  both 
perform  the  same  number  of  movemens.  Independently  of 
this,  we  may  easily  convince  ourselves  that  there  must  neces- 
sarily be  a  similar  motion  in  both  wings. 

If  we  move  one  of  the  wings  of  an  insect  recently  killed, 
we  shall  find  that  a  similar  movement  is  given,  in  a  certain 
degree,  to  the  other  corresponding  wing  ;  if  we  extend  one 
wing  laterally,  the  other  is  also  extended,  if  we  raise  one  up, 
the  other  rises.    The  wasp  is  well  suited  for  this  experiment. 

Still,  in  captive  flight,  certain  insects  can  perform  great 
movements  with  one  of  their  wings,  while  the  other  only  exe- 
cutes slight  vibrations.  The  dung-fly,  for  instance,  usually 
affects  this  kind  of  alternate  flight ;  when  it  is  held  with  the 
forceps,  its  two  wings  rarely  move  together.  The  sudden- 
ness and  the  unforeseen  condition  of  these  alternations,  and 
the  violent  deviations  which  they  give  to  the  axis  of  the  body, 
have  prevented  us  from  taking  the  simultaneous  tracings  of 
the  movement  of  its  two  wings,  and  from  ascertaining  whether 
the  synchronism  continues  under  these  conditions,  in  spite  of 
the  unequal  amplitude  of  the  movements. 

The  preceding  figures  show  the  regular  periodicity  of  the 
movements  of  insect  flight,  but  they  also  prove  that  the 
graphic  method  cannot  represent  the  whole  course  of  the  wing, 
for  this  organ  can  only  be  tangential  to  a  certain  portion  of 
the  surface  of  the  cylinder.  Whatever  may  be  the  movements 
18 


186 


ANIMAL  MECHANISM. 


which  the  wing  describes,  its  point  evidently  moves  on  the 
surface  of  a  sphere,  the  radius  of  which  is  the  length  of  the 
wing,  and  the  centre  at  the  point  of  attachment  of  this  organ 
with  the  mesothorax.  But  a  sphere  can  only  touch  a  plane  or 
ronvex  surface  at  one  point ;  thus,  we  only  obtain  a  number 
of  points  for  a  series  of  revolutions  of  the  wing,  if  the  turn- 
nig  cylinder  be  only  tangential  to  the  extremity  of  the  wing. 
More  complicated  tracings  can  only  be  obtained  by  more 
extensive  contacts,  in  which  the  wing  bends,  and  thus  rubs 
a  portion  of  its  surfaces  or  its  edges  on  the  blackened  paper. 

We  will  explain  the  means  by  which  the  graphic  method 
can  serve  to  determine  the  movements  of  the  wing,  but  let 
us  first  show  the  results  obtained  by  another  method,  in 
order  to  render  the  explanation  more  clear. 

2.  Optical  method  of  the  determination  of  the  movements  of 
the  wing. — Having  being  convinced  by  the  former  experi- 
ments, of  the  regular  periodicity  of  these  movements,  we  have 
thought  it  possible  to  determine  their  nature  by  the  eye.  In 
fact,  if  we  can  attach  a  brilliant  spot  to  the  extremity  of  the 
wing,  this  spot  passing  continually  through  the  same  space 
would  leave  a  luminous  trace  which  would  produce  a  figure 
completely  regular,  and  free  from  the  deformity  incident  to 
that  effected  by  the  friction  on  the  cylinder.  This  optical 
method  has  already  been  employed  for  a  similar  purpose  by 
Wheatstone,  who  placed  brilliant  metallic  balls  on  rods  pro- 
ducing complex  vibrations,  and  thus  obtained  luminous 
figures  varying  according  to  the  different  combinations  of  the 
vibrating  movements. 

By  fixing  a  small  piece  of  gold-leaf  at  the  extremity  of  the 
wing  of  a  wasp,  and  throwing  upon  it  a  ray  of  the  sun  while 
the  insect  was  executing  the  movements  of  flight,  we  have 
obtained  a  brilliant  image  of  the  successive  positions  of  the 
wing,  which  gave  nearly  the  appearance  represented  in 
fig.  71. 

This  figure  shows  that  the  point  of  the  wing  describes  a 
very  elongated  figure  8  ;  sometimes,  indeed,  the  wing  seems 
to  move  entirely  in  one  plane,  and  the  instant  afterwards  the 
terminal  loops  which  form  the  8  are  seen  to  open  more  find 
more.     When  the  opening  becomes  very  large,  one  of  the 


FLIGHT  OF  INSECTS.  187 

loops  usually  predominates  over  the  other ;  it  is  generally  the 
lower  one  which  increases  while  the  upper  diminishes.  Indeed, 
by  a  still  greater  opening,  the  figure  is  occasionally  trans- 
formed into  an  irregular  ellipse,  at  the  extremity  of  which  we 
can  recognise  a  vestige  of  the  second  loop. 


Fig.  71  —  Appearance  of  a  wasp,  the  extremity  of  each  of  whose  larger 
wings  has  been  gilded.  The  insect  is  supposed  to  be  placed  in  a  sun- 
beam. 


We  thought  that  we  had  been  the  first  to  point  out  the  form 
of  the  trajectory  of  the  wing  of  the  insect,  but  Dr.  J.  B.  Petti- 
grew,  an  English  author,  informs  us  that  he  had  already 
mentioned  this  figure  of  8  appearance  described  by  the  wing, 
and  had  represented  it  in  the  plates  of  his  work.*  It  will 
be  seen  presently  that,  notwithstanding  this  apparent  agree- 
ment, our  theory  and  that  of  Dr.  Pettigrew  differ  materially 
from  each  other. 

Changes  of  the  plane  of  the  wing. — The  luminous  appearance 
given  during  flight  by  the  gilded  wing  of  an  insect,  shows 

*  On  the  Mechanical  Appliances  by  which  Flight  is  Maintained  in  the 
Animal  Kingdom.    Transact,  of  Linnean  Society,  1S67,  p.  233. 


188 


ANIMAL  MECHANISM. 


besides,  that  during  the  alternate  movements  of  flight,  the 
plane  of  the  wing  changes  its  inclination  with  respect  to  the 
axis  of  the  insect's  body,  and  that  the  upper  surface  of  the 
wing  turns  a  little  backward  during  the  period  of  ascent, 
whilst  it  is  inclined  forward  a  little  during  its  descent. 

If  we  gild  a  large  portion  of  the  upper  surface  of  a  wasp's 
wing,  taking  precautions  that  the  gold-leaf  should  be  limited 
to  this  surface  only,  we  see  that  the  animal,  placed  in  the  sun's 
rays,  gives  the  figure  of  8  with  a  very  unequal  intensity  in 
the  two  halves  of  the  image,  as  represented  in  fig.  7 1 .  The 
figure  printed  thus  8  gives  an  idea  of  the  form  which  is  then 
produced,  if  we  consider  the  thick  stroke  of  this  character  as 
corresponding  with  the  more  brilliant  portion  of  the  image, 
and  the  thin  stroke  as  representing  the  part  which  is  less 
bright. 

It  is  evident  that  the  cause  of  the  phenomenon  is  to  be 
found  in  a  change  in  the  plane  of  the  wing,  and  consequently 
in  the  incidence  of  the  solar  rays ;  being  favourable  to  their 
reflection  during  the  period  of  ascent,  and  unfavourable  during 
the  descent.  If  we  turn  the  animal  round,  so  as  to  observe 
the  luminous  figure  in  the  opposite  direction,  the  8  will  then 
present  the  unequal  splendour  of  its  two  halves,  but  in  the 
inverse  direction;  it  becomes  bright  in  the  portion  before 
relatively  obscure,  and  vice  vers  A. 

We  shall  find  in  the  employment  of  the  graphic  method, 
new  proofs  of  changes  in  the  plane  of  the  wing  during  flight. 
This  phenomenon  is  of  great  importance,  for  in  it  we  seem  to 
find  the  proximate  cause  of  the  motive  force  which  urges  for- 
ward the  body  of  the  insect. 

In  order  to  verify  the  preceding  experiments,  and  to  assure 
ourselves  still  more  of  the  reality  of  the  displacement  of  the 
wing,  which  the  optical  method  has  revealed  to  us,  we  have 
introduced  the  extremity  of  a  small  pointer  into  the  interior  of 
the  figure  8  described  by  the  wing,  and  we  have  proved  that 
in  the  middle  of  these  loops  there  really  exist  free  spaces  of 
the  form  of  a  funnel,  into  which  the  pointer  penetrates  with- 
out meeting  the  wing,  whilst,  if  we  try  to  pass  the  intersection 
where  the  lines  cross  each  other,  the  wing  immediately  strikes 
against  the  pointer,  and  the  flight  is  interrupted. 


FLIGHT  OF  INSECTS. 


Ib9 


Graphic  m.cthod  employed  for  the  determination  of  the  move- 
ments of  the  wing. — The  preceding  experiments  throw  great  light 
on  the  traces  which  we  obtain  by  the  friction  of  the  insect's 
wing  against  the  blackened  cylinder.  Although  the  figures 
thus  produced  are  for  the  most  part  incomplete,  we  are  able, 
by  means  of  their  scattered  elements,  to  reconstruct  the  figure 
which  has  been  shown  by  the  optical  method. 

It  is  to  be  remarked  that  without  sensibly  interfering  with 
the  movements  of  the  wing,  we  can  obtain  traces  of  seven  or 
eight  millimetres  when  the  wing  is  rather  long.  The  slight 
flexure  to  which  the  wing  is  suljected  allows  it  to  remain  in 
contact  with  the  cylinder  to  that  extent ;  we  thus  obtain  a 
partial  tracing  of  the  movement ;  so  that  if  we  are  careful  to 
produce  the  contact  of  the  wing  with  the  cylinder  in  different 
parts  of  the  course  passed  through  by  the  limb,  we  obtain  a 
series  of  partial  tracings  which  are  complementary  to  each 
other,  and  thus  allow  us  to  deduce  from  them  the  form  of  a 
perfect  curve  of  the  revolution  of  a  wing.  Suppose,  then, 
that  in  fig.  71,  the  curve  described  by  the  gilded  wing  is 
divided  by  horizontal  lines  into  three  zones  :  the  upper  one, 
formed  by  the  upper  loop  ;  that  in  the  middle,  comprehending 
the  two  branches  of  the  8.  crossing  each  other  and  forming  a 
sort  of  X  ;  the  lower  one  including  the  lower  loop. 

By  registering  the  movement  of  the  middle  zone,  we  get 


■I    l   'I   ".' .   r    ,  • 


Fjo.  72.-  -Tracintr  of  tbe  middle  region  of  the  course  of  the  wing  of  a  bee, 
showing  the  crossing  of  the  two  branches  of  the  8.  One  of  the  branches 
is  prolonged  rather  far,  but  still  the  tracing  of  the  lower  loop  has  nut  been 
produced. 

figures  somewhat  resembling  each  other,  in  which  the  lines, 
placed  obliquely  with  respect  to  each  other,  cut  each  other. 
This  is  the  case  in  fig.  72,  the  middle  region  of  the  tracing 
of  a  bee,  and  in  fig.  73,  the  middle  portion  of  that  of  a 
humming-bird  moth. 


190  ANIMAL  MECHANISM. 


The  upper  zone  of  the  revolution  of  the  wing  gives  tracings 
analogous  with  that  of  fig.  74,  in  which  t'-e  upper  loops  of  the 
8  are  plainly  visible.    The  tracings  of  the  zone  which  corre 


Fio.  73.— Tracing  of  the  middle  zone  in  the  course  described  by  the  wii  g  of 
a  humming-bird  moth.  The  numerous  strokes  ot  which  this  tracing  is 
formed,  arise  from  the  extremity  of  the  wing  being  fringed  and  present- 
ing a  rough  surface. 


sponds  with  the  lower  course  of  the  wing  give  also  loops  like 
those  of  the  upper  arch  (fig.  75  shows  a  specimen  of  them)  ; 
so  that  the  fignre  8  of  the  tracing  can  be  reproduced  hy 


Fig.  74. — This  figure  shows,  in  the  tracing  made  by  a  wasp,  the  upper  oop, 
and  all  the  extent  of  one  branch  of  the  8.  The  middle  part  of  tins 
branch  is  merely  dotte<l  because  of  the  feeble  friction  of  the  wing. 


bringing  together  the  three  fragments  of  its  course  successively 
obtained. 

If  we  could  only  once  procure  the  entire  tracing  formed  by 
the  wing  of  an  insect,  we  should  then  get  a  figure  identical 
with  that  which  our  learned  writer  on  acoustics,  Kcenig,  was 
the  first  to  obtain  with  a  Wheatstone  rod  tuned  to  the  octave, 
that  is  to  say,  describing  an  8  in  space.  This  typical  form  is 
represented  in  fig.  76.    We  shall  tee  that  the  graphic  method 


FLIGHT  OF  INSECTS. 


191 


is  adapted  to  other  experiments  intended  to  verify  those  which 
we  have  already  made  by  other  means.  By  varying  the  inci- 
dence of  the  wing  on  the  revolving  cylinder,  we  can  foretell 
what  will  be  the  figure  traced,  if  it  be  true  that  the  wing 
really  describes  the  form  of  an  8.    Thus,  if  we  obtain  a  figure 


Fig.  75.— Tracings  of  the  wing  of  a  wasp  ;  several  of  the  lower  loops  are 
distinctly  seen  This  tracing  was  obtained  by  holding  the  insect  so  as 
to  rub  the  cylinder  by  the  hinder  point  of  the  wing,  which  gives  very  ex- 
tended curves. 


conformable  to  that  which  we  have  foreseen,  it  will  be  an 
evident  proof  of  the  reality  of  these  movements. 


Fi<"!.  76.—  Tracing  of  a  Wheatstone's  kaleidophone  rod.  tuned  to  the  octave, 
that  is  tosay.  vibrating  twice  transversely  for  each  longitudinal  vibration. 
(This  figure'  is  taken  from  R.  Kojni;;.  The  slackening  speed  of  the 
cylinder  produces  an  approximation  of  the  curves  towards  the  end  of  the 
figure. 

Let  us  suppose  that  the  wing  of  the  insect,  instead  of 
touching  the  cylinder  with  its  point,  as  we  have  seen  just 
now,  brushes  it  with  one  of  its  edges  ;  and  let  us  admit  for 
an  instant  that  the  8  described  by  the  wing  is  so  lengthened 
that  it  departs  but  slightly  from  the  plane  passing  through 
the  vertical  axis  of  this  figure.  If  we  press  the  wing  slightly 
against  the  cylinder  the  contact  will  be  continuous,  and  the 
tracing  uninterrupted ;  but  the  figure  obtained  will  no 
longer  be  an  8  ;  if  the  cylinder  be  immovable  it  will  be  an 
arc  of  a  circle,  whose  concavity  will  be  turned  towards  the 
point  of  insertion  of  the  wing,  a  point  which  will  occupy  pre- 
cisely the  centre  of  the  curvs  described. 


192 


ANTMAL  MECHANISM. 


If  the  cylinder  revolve,  the  figure  will  be  spread  out  like 
the  oscillation  of  a  tuning-fork  registered  under  the  same 
conditions,  and  we  shall  obtain  a  tracing  more  or  less  ap- 
proaching in  form  to  that  which  is  represented  in  fig.  77. 


Fig.  77.- -Tracing'  obtained  with  the  winer  of  a  bee  oscillating  in  a  plane 
which  is  sensibly  tangential  to  the  generatrix  of  tue  registering  cylinders. 

This  form,  which  theory  enables  us  to  predict,  is  always 
produced  when  the  plane  in  which  the  wing  moves  is  tan- 
gential to  the  generatrix  of  the  cylinder. 

But  in  examining  these  tracings  we  easily  recognise  changes 
in  the  thickness  of  the  stroke — parts  which  appear  to  have  been 
made  by  a  greater  or  less  friction  of  the  wing  on  the  cylin- 
der ;  we  here  find  a  new  and  certain  proof  of  the  existence  of 
a  movement  in  the  form  of  an  8,  as  we  now  propose  to  show 
by  a  synthetic  method. 

Let  us  take  aWheatstone's  rod  tuned  to  the  octave  ;  let  us  fix 
on  it  the  wing  of  an  insect  as  a  style,  and  let  us  trace  the  vibra- 
tions which  it  executes.  We  shall  obtain,  if  the  cylinder  be 
motionless,  figures  of  8  when  the  wing  touches  the  paper  by 
its  point  applied  perpendicularly  to  its  surface ;  and  if  the 
cylinder  revolve,  we  shall  have  lengthened  figures  of  8. 

We  may  obtain,  with  a  rod  tuned  to  the  octave,  tracings 
identical  with  those  given  by  the  insect ;  of  which  a  proof  is 
afforded  by  the  comparison  of  the  two  following  figures  :  — 


Fig.  78.-- Tracings  of  a  wa«p  ;  the  insect  is  h^ld  so  that  its  wing  totiches 
tue  cylinder  by  its  point,  and  traces  especially  the  upper  loop  of  the  6. 


FLIGHT  OF  INSECTS. 


193 


The  graphic  method  also  furnishes  us  with  the  proof  of 
changes  in  the  plane  of  the  wing  of  the  insect  during  the 
various  instants  of  its  revolutions. 


Fig.  79. — Tracings  of  a  Wheatstone  rod  tuned  to  the  octave,  furnished 
with  the  wing  of  a  wasp,  and  arranged  so  as  to  register  especially  the 
upper  loop  of  the  8. 


Fig.  80  shows  the  tracing  furnished  by  a  wing  of  a  hum- 
ming-bird moth,  arranged  so  as  to  touch  the  cylinder  with  its 
posterior  edge.  By  bringing  the  insect  not  too  near,  we  can 
succeed  in  producing  only  intermittent  contacts ;  these  take 
place  at  the  moment  when  the  wing  describes  that  part  of  the 
loops  of  the  8  whose  convexity  is  tangential  to  the  cylinder. 
The  contacts  which  occupy  the  upper  half  of  the  figure  alter- 
nate with  those  occupying  the  lower  half.  It  is  seen,  besides, 
that  it  is  not  the  same  surface  of  the  wing  which  produces 
these  two  kinds  of  friction.    In  fact,  it  is  evident  that  the 


jb  io.  80. — Tracings  of  the   movements  of  the  wing  of  a  humming-bird 
moth  (macroglossa)  rubbing  on  the  cylinder  by  its  lower  edge. 


marks  of  the  upper  half,  each  formed  of  a  series  of  oblique 
strokes,  are  produced  by  the  contact  of  a  fringed  border,  while 
the  contacts  of  the  lower  part  are  produced  by  another  portion 
of  the  wring  which  presents  a  region  unprovided  with  fringes, 
and  leaves  a  whiter  trace  w-ith  boundaries  better  defined. 


194 


ANIMAL  MECHANISM. 


These  changes  of  plane  are  only  found  in  great  movements 
of  the  wing.  This  is  an  important  fact,  for  it  will  explain  to 
us  the  method  of  their  production.  Fig.  81  was  furnished 
like  fig.  80  by  the  movements  of  the  wing  of  a  moth  (macro- 
glossa) ;  but  on  account  of  its  fatigue  these  movements  had 
lost  nearly  all  their  amplitude. 


Fig.  81.--Traciner  of  the  wing  of  a  fatigued  macroglossa.    The  figure  8  is 
no  longer  to  be  seen,  but  only  a  simple  pendular  oscillation. 

We  see  only  in  this  figure  a  series  of  pendular  oscillations, 
showing  that  the  wing  merely  rose  and  fell  without  changing 
its  plane.  The  bright  line  which  borders  the  ascending  and 
upper  parts  of  these  curves  is  explained  by  the  alternate 
flexions  of  the  wing  as  it  rubs  upon  the  paper,  and  shows 
that  the  upper  surface  was  rough,  and  left  a  distinct  trace, 
while  the  lower  surface  presented  no  similar  roughness. 

3.  Direction  of  the  movement  of  the  wing.  —  One  more  very 
important  element  is  required  to  give  us  a  complete  knowledge 
of  the  movements  which  the  insect's  wing  executes  in  its  flight. 
The  optical  method,  while  it  shows  us  all  the  points  in  the 
curve  described  by  the  gilded  extremity  of  the  wing,  does  not 
indicate  the  direction  in  which  this  revolution  is  accomplished  ; 
whatever  may  be  the  direction  in  which  the  wing  moves  in  its 
orbit,  the  luminous  image  which  it  affords  must  be  always 
the  same. 

A  very  simple  method  has  furnished  a  solution  of  this  new 
question.  Let  fig.  82  be  the  luminous  image  furnished  by 
the  movements  of  the  right  wing  of  an  insect.  The  direction 
of  these  movements  which  the  eye  cannot  follow  is  indicated 
by  arrows. 

To  determine  the  direction  of  these  movements,  we  take  a 
small  rod  of  polished  glass  and  blacken  it  with  the  smoke  of 
a  wax  taper ;  when  holding  the  rod  at  right  angles  to  the 
direction  in  which  the  wing  moves,  we  present  the  blackened 


FLIGHT  OF  INSECTS. 


end  to  (a),  that  is  to  say,  in  front  of  the  lower  loop.  We 
endeavour  to  pass  this  point  into  the  interior  of  the  course 
described  by  the  wing ;  but  as  soon  as  it  enters  this  region, 
the  rod  receives  a  series  of  shocks  from  the  wing,  which  rubs 
on  its  surface,  and  wipes  off  the  soot  which  covered  it.  When 
we  examine  the  surface  of  the  glass,  we  see  that  the  soot  has 
been  removed  only  on  the  upper  part,  which  shows  that  at 
the  point  (a)  of  its  course,  the  wing  is  descending.  The 
same  experiment  being  repeated  in  (a'),  that  is  to  say,  in  the 
hinder  part  of  the  orbit  of  the  wing,  it  is  found  that  the  rod 
has  been  rubbed  beneath  ;  so  that  the  wing  at  a  was  ascending. 
In  the  same  manner  it  may  be  shown  that  the  wing  rises  at 
b  and  descends  at  b' . 


Fio.  82 —Detenu  nation  of  the  direction  of  the  movements  of  an  insect's 
wing. 

We  now  know  all  the  movements  executed  by  an  insect's  wing 
during  its  revolution,  as  well  as  the  double  change  of  plane  which 
accompanies  them.  The  knowledge  of  this  change  of  plane 
was  given  to  us  by  the  unequal  brightness  of  the  two  branches 
of  the  luminous  8.  Thus  we  may  feel  assured  that  in  the 
course  of  the  descending  wing,  that  is  from  b'  to  a  in  fig.  82, 
the  upper  surface  of  the  wing  turns  slightly  forward,  while 
from  a  to  b,  that  is,  in  ascending,  this  surface  turns  a  little 
backwards. 


196 


ANIMAL  MECHANISM. 


CHAPTER  II. 

MECHANISM  OF  THE  FLIGHT  OF  INSECTS. 

Causes  of  the  movements  of  the  wings  of  insects — The  muscles  only  give 
a  motion  to  and  fro,  the  resistance  of  the  air  modifies  the  course  of 
the  wing— Artificial  representation  of  the  movements  of  the  insect's 
wing  — Of  the  propulsive  effect  of  the  wings  of  insects — Construc- 
tion of  an  artificial  insect  which  moves  horizontally— Change  in  the 
plane  in  flight. 

1.  Causes  of  the  movements  of  the  wing. — These  exceedingly 
complicated  movements  would  induce  us  to  suppose  that  there 
exists  in  insects  a  very  complex  muscular  apparatus,  but 
anatomy  does  not  reveal  to  us  muscles  capable  of  giving-  rise 
to  all  these  movements.  We  scarcely  find  any  but  elevating 
and  depressing  forces  in  the  muscles  which  move  the  wing ; 
besides  this,  when  we  examine  more  closely  the  mechanical 
conditions  of  the  flight  of  the  insect,  we  see  that  an  upward 
and  downward  motion  given  by  the  muscles  is  sufficient  to  pro- 
duce all  these  successive  acts,  so  well  co-ordinated  with  each 
other ;  the  resistance  of  the  air  effecting  all  the  other  move- 
ments. 

If  we  take  off  the  wing  of  an  insect  (fig.  83),  and  holding 
it  by  the  small  joint  which  connects  it  with  the  thorax,  expose 
it  to  a  current  of  air,  we  see  that  the  plane  of  the  wing  is 


Fio.  83.  — Structure  of  an  insect's  wing. 


inclined  more  and  more  as  it  is  subjected  to  a  more  powerful 
impulse  of  the  wind.  The  anterior  nervure  resists,  but  the 
membranous  portion  which  is  prolonged  behind  bends  on 
account  of  its  greater  pliancy.   If  we  blow  upon  the  upper  sur- 


MECHANISM  OF  INSECT  FLIGHT. 


107 


face  of  the  wing,  we  see  this  surface  carried  backwards,  while 
by  blowing  on  it  from  beneath,  we  turn  the  upper  surface 
forwards.  In  certain  species  of  insects,  according  to  Felix 
Plateau,  the  wing  resists  the  pressure  of  the  air  acting  from 
below  upwards,  more  than  that  exerted  in  an  opposite 
direction. 

Is  it  not  evident,  that  in  the  movements  which  take  place 
during  flight,  the  resistance  of  the  air  will  produce  upon  the 
plane  of  the  wing  the  same  effects  as  the  currents  of  air  which 
we  have  just  employed  ?  The  changes  in  the  plane,  caused 
by  the  resistance  of  the  air  under  these  conditions,  are  pre- 
cisely those  which  are  observed  in  flight.  We  have  seen  that 
the  descending  wing  presents  its  anterior  surface  forwards, 
which  is  explained  by  the  resistance  of  the  air  acting  from 
below  upwards ;  while  the  ascending  wing  turns  its  upper  sur- 
face backwards,  because  the  resistance  of  the  air  acts  upon  it 
from  above  downwards. 

It  is,  therefore,  not  necessary  to  look  for  special  muscular 
actions  to  produce  changes  in  the  plane  of  the  wing;  these, 
in  their  turn,  will  give  us  the  key  to  the  oblique  curvilinear 
movements  which  produce  the  figure  of  8  course  followed  by 
the  insect's  wing. 

Let  us  return  to  fig.  82  :  the  wing  which  descends  has  at 
the  same  time  a  forward  motion  ;  therefore,  the  inclination 
taken  by  the  plane  of  the  wing,  under  the  influence  of  the 
resistance  of  the  air,  necessarily  causes  the  oblique  descent 
from  b'  to  a.  An  inclined  plane  which  strikes  on  the  air  has 
a  tendency  to  move  in  the  direction  of  its  own  inclination. 

Let  us  suppose,  then,  that  the  wing  only  rises  and  falls  by 
its  muscular  action ;  the  resistance  of  the  air,  by  pressing  on 
the  plane  of  the  wing,  will  force  the  organ  to  move  forward 
while  it  is  being  lowered.  But  this  deviation  cannot  be 
effected  without  the  nervure  being  slightly  bent.  The  force 
which  causes  the  wing  to  deviate  in  a  forward  direction  neces- 
sarily varies  in  intensity  according  to  the  rapidity  with  which 
the  organ  is  depressed.  Thus,  when  the  wing  towards  the 
end  of  its  descending  course  moves  more  slowly,  we  shall 
see  the  nervure,  as  it  is  bent  with  less  force,  bring  the  wing 

backwards  in  a  curvilinear  direction.      Thus  we  explain 
19 


198 


ANIMAL  MECHANISM. 


naturally  the  formation  of  the  descending  branch  of  the  8 
passed  through  by  the  wing. 

The  same  theory  applies  to  the  formation  of  the  ascending 
branch  of  this  figure.  In  short,  a  kind  of  pendular  oscilla^ 
tion  executed  by  the  nervure  of  the  wing  is  sufficient,  to- 
gether with  the  resistance  of  the  air,  to  give  rise  to  all  the 
movements  revealed  to  us  by  our  experiments. 

2.  Artificial  representation  of  the  movements  of  the  insect's  wing. 
— These  theoretical  deductions  require  experimental  verifica- 
tion, in  order  that  they  may  be  thoroughly  borne  out.  We 
have  succeeded  in  obtaining  the  following  results  : — 

Let  fig.  84  be  an  instrument,  which,  by  means  of  a  multi- 
plying wheel  and  a  connecting  rod,  gives  to  a  flexible  shaft 
rapid  to  and  fro  movements  in  a  vertical  plane.  Let  us  take 
a  membrane  similar  to  that  in  the  wings  of  insects,  and  fix  it 
to  this  shaft,  which  will  then  represent  the  main  rib  of  the 
wing ;  we  shall  see  this  contrivance  execute  all  the  move- 
ments which  the  wing  of  the  insect  describes  in  space. 

If  we  illuminate  the  extremity  of  this  artificial  wing,  we 
shall  see  that  its  point  describes  the  figure  8,  like  a  real  wing ; 
we  shall  observe  also  that  the  plane  of  the  wing  changes 
twice  during  each  revolution  in  the  same  manner  as  in  the 
insect  itself.  But  in  the  apparatus  which  we  now  employ, 
the  movement  communicated  to  the  wing  is  only  upwards 
and  downwards.  Were  it  not  for  the  resistance  of  the  air, 
the  wing  would  only  rise  and  fall  in  a  vertical  plane ;  all 
these  complicated  movements  are  due  therefore  only  to  the 
resistance  presented  by  the  air.  Consequently,  it  is  this 
which  bends  the  main  rib  of  the  wing,  turning  it  in  a  direc- 
tion perpendicular  to  the  plane  in  which  its  oscillation  is 
effected. 

But  if  the  wing  be  pushed  aside  from  its  main-rib  at  each 
of  its  alternate  movements,  it  is  evident  that  the  air,  acted 
upon  by  this  wing,  will  receive  an  impulse  in  an  opposite 
direction ;  that  is  to  say,  it  will  escape  at  the  side  of  the 
flexible  portion  of  the  wing,  and  cause  in  this  direction  a 
current  of  air.  It  is  seen,  in  figure  84,  that  a  candle  placed 
by  the  bide  of  the  thin  edge  of  the  wing,  is  strongly  blown 
by  the  current  of  air  which  is  produced.    In  front  of  the  wing, 


MECHANISM  OF  INSECT  FLIGHT. 


199 


on  the  contrary,  the  air  will  he  drawn  forwards,  so  that  the 
flame  of  another  candle  placed  in  front  of  t lie  nervure  will  he 
strongly  drawn  towards  it. 


Fig.  84. — Artificial  representation  of  the  movements  of  an  insect's  wing. 


3.  Of  the  propulsive  action  of  the  wings  of  insects. — In  the 
same  manner  as  the  squib  moves  in  the  opposite  direction  to 
the  jet  of  flame  which  it  throws  out,  the  insect  propels  itself 
in  the  course  opposed  to  the  current  of  air  produced  by  the 
movement  of  its  wings. 

Each  stroke  of  the  wing  acts  on  the  air  obliquely,  and 
neutralizes  its  resistance,  so  that  a  horizontal  force  results, 


200 


ANIMAL  MECHANISM. 


which  impels  the  insect  forwards.  This  resultant  acts  in  the 
descent  of  the  wing,  as  well  as  in  its  upward  movement,  so 
that  each  part  of  the  oscillation  of  the  wing  has  an  action 
favourable  to  the  propulsion  of  the  animal. 

An  effect  is  produced  analogous  with  that  which  takes  place 
when  an  oar  is  used  in  the  stern  of  a  boat  in  the  action  of 
sculling.  Each  stroke  of  the  oar,  which  presents  an  inclined 
plane  to  the  resisting  water,  divides  this  resistance  into  two 
forces :  one  acts  in  a  direction  opposed  to  the  motion  of  the 
oar,  the  other,  in  a  direction  perpendicular  to  that  movement, 
and  it  is  the  latter  which  impels  the  boat. 

Most  of  the  propellers  which  act  in  water  overcome  the 
resistance  of  the  fluid  by  the  action  of  an  inclined  plane. 
The  tail  of  the  fish  produces  a  propulsion  of  this  kind ;  that 
of  the  beaver  does  the  same,  with  this  difference,  that  it 
oscillates  in  a  vertical  plane.  Even  the  screw  may  be  con- 
sidered as  an  inclined  plane,  whose  movement  is  coDtinuous, 
and  always  in  the  same  direction. 


FiO.  85  — Representation  of  the  changes  in  the  plane  of  the  insect's  wing. 

If  we  wish  to  represent  the  inclination  of  the  plane  of  the 
wing  at  the  different  parts  of  its  course,  we  shall  obtain 
fig.  85,  in  which  the  arrows  indicate  the  direction  of  the 
course  of  the  wing,  and  the  lines,  whether  dotted  or  full, 
show  the  inclination  of  its  ^lane. 

After  this,  we  need  only  show  the  figure  traced  by  Dr.  Pet- 
tigrew  in  his  work  on  flight,  to  prove  how  far  the  ideas  of 
this  English  writer  differ  from  ours. 

The  trajectory  of  the  wing  is  represented  by  Dr.  Petti- 
grew  by  means  of  fig.  86.  Four  arrows  indicate,  according 
to  this  writer,  the  direction  of  movements  in  the  different  por- 


MECHANISM  OF  INSECT  FLIGHT 


201 


tions  of  this  trajectory.  These  arrows  are  in  the  same 
direction,  and  this  first  fact  is  opposed  to  the  experiment 
described  in  page  195,  where  we  have  investigated  the  direc- 
tion of  the  movement  of  the  wing,  and  have  found  it  pass  in 
opposite  directions  in  the  two  branches  of  the  8.  In  order  to 
explain  the  form  which  he  assigns  to  this  trajectory,  Dr.  Pet- 
tigrew  admits  that  in  its  passage  from  right  to  left,  the  wing 
describes  by  its  thicker  edge  the  thick  branch  of  the  8.  and  the 


thin  branch  by  its  narrow  edge.  The  crossing  of  the  8  there- 
fore would  be  formed  by  a  complete  reversal  of  the  plane  of 
the  wing  during  one  of  the  phases  of  its  revolution.  In  fact, 
the  author  seems  to  perceive  in  this  reversal  of  the  plane,  an 
action  similar  to  that  of  a  screw,  of  which  the  air  would  form 
the  nut.  We  will  not  dwell  any  longer  on  this  theory,  but 
we  have  deemed  it  necessary  to  bring  it  forward,  in  con- 
sequence of  the  appeal  which  has  been  made  to  us. 

4.  Artificial  representation  of  an  insect's  flight. — In  order  to 
render  the  action  of  the  wing  and  the  effects  of  the  resistance 
of  the  air  more  intelligible,  we  have  made  use  of  the  following 
apparatus : — 

Let  fig.  87  represent  two  artificial  wings  composed  of  a  rigid 
main-rib  connected  with  a  flexible  membrane,  composed  of 
gold-beater's  skin,  strengthened  by  fine  nervures  of  steel ;  the 
plane  of  these  wings  is  horizontal ;  a  system  of  bent  levers 
raises  or  lowers  them  without  giving  them  any  lateral  mo- 
tion. 

The  movement  of  the  wings  is  caused  by  a  little  copper 
drum,  in  which  the  air  is  alternately  condensed  and  rarefied 
by  the  action  of  a  pump.     The  circular  surfaces  of  this  drum 


Fig.  86.— Trajectory  of  the  wing. 


MECHANISM  OF  INSECT  FLIGHT. 


203 


are  formed  of  india-rubber  membranes  connected  with  the 
two  wings  by  bent  levers ;  the  air  when  compressed  or  rarefied 
gives  to  these  flexible  membranes  powerful  and  rapid  move- 
ments, which  are  transmitted  to  both  wings  at  the  same  time. 

A  horizontal  tube,  balanced  by  a  counterpoise,  allows  the 
apparatus  to  turn  upon  a  central  axis,  and  serves  at  the  same 
time  to  conduct  the  air  into  the  drum,  which  produces  the 
motion.  This  axis  is  formed  of  a  kind  of  mercurial  gaso- 
meter, which  hermetically  seals  the  air  conduits,  while  it  allows 
the  instrument  to  turn  freely  in  a  horizontal  plane. 

Thus  arranged,  the  apparatus  shows  the  mechanism  by 
which  the  resistance  of  the  air,  combined  with  the  movements 
of  the  wing,  produces  the  propulsion  of  the  insect. 

If  we  Set  in  motion  the  wings  of  the  artificial  insect  by 
means  of  the  air-pump,  wre  see  the  apparatus  soon  begin  to 
revolve  rapidly  around  its  axis.  The  mechanism  of  the  mo- 
tion of  the  insect  is  clearly  illustrated  by  this  experiment, 
entirely  confirming  the  theories  which  we  have  deduced  from 
optical  and  graphic  analysis  of  the  movements  of  the  wing 
during  flight. 

It  may  be  asked  whether  the  figure  of  8  movements  de- 
scribed by  the  wing  of  a  captive  insect  are  also  produced  when 
the  creature  flies.  We  have  just  seen  that  the  bending  of  the 
main-rib  is  entirely  due  to  the  force  which  carries  the  insect 
forward  when  it  has  become  free.  We  might  therefore  sup- 
pose that  the  main-rib  of  the  wing  does  not  yield  to  this  force 
when  the  insect  flies  freely,  and  that  the  resulting  horizontal 
force  is  shown  only  by  the  impulsion  of  the  whole  of  the  insect 
forwards. 

If,  after  having  gilded  the  wing  of  the  artificial  insect,  we 
look  at  the  luminous  image  produced  during  its  flight,  we  still 
see  the  figure  of  8  remaining,  provided  the  flight  be  not  too 
rapid.  In  fact,  this  figure  is  modified  by  the  movement  of 
the  apparatus ;  it  becomes  more  extended,  and  resembles  the 
8  registered  on  a  revolving  cylinder,  but  it  is  not  reduced  to  a 
simple  pendular  curve,  which  would  be  the  case  if  the  main- 
rib  were  always  rigid.  We  can  understand  that  this  may  be 
caused  by  the  inertia  of  the  apparatus,  which  cannot  be 
allected  by  the  variable  movements  which  each  stroke  of  ti  e 


204 


ANIMAL  MECHANISM. 


wing  tends  to  bring  to  bear  upon  it.  The  artificial  insect, 
when  once  set  in  motion,  is  sometimes  before,  and  at  others 
behind  the  horizontal  force  developed  by  the  wing :  on  this 
account  the  rib  of  the  wing  is  forced  to  bend,  because  the 
mass  to  be  moved  does  not  obey  instantaneously  the  resulting 
horizontal  force  which  the  wing  derives  from  the  resistance  of 
the  air.  The  same  phenomenon  must  take  place  in  the  flight 
of  a  real  insect. 

5.  Plane  of  oscillation  of  an  insect's  wing. — The  apparatus 
which  has  just  been  described  does  not  yet  give  a  perfect  idea 
of  the  mechanism  of  insect  flight.  We  have  been  compelled, 
for  the  sake  of  explaining  the  movements  of  the  wing  more 
easily,  to  suppose  that  its  oscillation  is  made  from  above 
downwards ;  that  is  to  say,  from  the  back  of  the  insect  towards 
its  lower  surface,  when  lying  horizontally  in  the  air. 

But  we  need  only  observe  the  flight  of  certain  insects,  the 
common  fly,  for  instance,  and  most  of  the  other  diptera, 
to  see  that  the  plane  in  which  the  wings  move  is  not  verti- 
cal, but,  on  the  contrary,  very  nearly  horizontal.  This  plane 
directs  its  upper  surface  somewhat  forward,  and  therefore 
the  main-rib  of  the  wing  corresponds  with  this  surface. 
Consequently,  it  is  from  below  upwards,  and  a  little  forward 
that  the  propulsion  of  the  insect  is  effected.  The  greater  part 
of  the  force  exerted  by  the  wing  will  be  employed  in  sup- 
porting the  insect  against  the  action  of  its  weight ;  the  rest  of 
this  impulse  will  carry  it  forward. 

By  changing  the  inclination  of  the  plane  of  oscillation  of  its 
wings,  which  can  be  done  by  moving  the  abdomen  so  as  to 
displace  the  centre  of  gravity,  the  insect  can,  according  to  its 
wishes,  increase  the  rapidity  of  its  forward  flight,  lessen  the 
speed  acquired,  retrograde,  or  dart  toward  the  side. 

It  is  easily  to  be  seen  that,  when  a  hymenopterous  insect 
flying  at  full  speed,  stops  upon  a  flower,  this  insect  directs  the 
plane  of  the  oscillation  of  its  wings  backwards  with  consider- 
able force. 

Nothing  is  more  variable,  in  fact,  than  the  inclination  of 
the  plane  in  which  the  wings  of  different  species  of  insects 
oscillate. 

I     The  diptera  fippear  to  us  to  have  this  plane  of  oscillation 


206 


ANIMAL  MECHANISM. 


Lvery  nearly  horizontal ;  in  the  hymenoptera,  the  wing  moves 
in  a  plane  of  nearly  45°  ,  but  the  lepidoptera  flap  their  wings 
almost  vertically,  after  the  manner  of  birds. 

In  order  to  render  the  influence  of  the  plane  of  oscilla- 
tion more  evident,  and  to  show  that  the  force  derived  from  the 
resistance  of  the  air  has  the  double  effect  of  raising  the  insect 
and  directing  its  course,  we  must  arrange  the  flight-instrument 
in  a  peculiar  manner.  It  will  be  necessary,  in  the  first  place, 
to  be  able  to  change  the  plane  of  oscillation  of  the  wings, 
which  is  effected  by  placing  the  drum  on  a  pivot  at  the  ex- 
tremity of  the  horizontal  tube,  at  the  end  of  which  it  turns. 
To  show  the  ascensional  force  which  is  developed  in  this  new 
arrangement,  the  instrument  must  no  longer  be  confined  to  a 
simple  movement  of  rotation  in  the  horizontal  plane,  but  it 
must  be  able  to  oscillate  in  a  vertical  plane  like  the  scale  beam 
of  a  balance. 

Fig.  88  shows  the  new  arrangement  which  we  have  given 
to  the  instrument  in  order  to  obtain  this  double  result. 

In  this  modification  of  the  apparatus,  the  air-pump  which 
constitutes  the  moving  force  is  retained  ;  as  is  also  the  turn- 
ing column  which  moves  in  the  mercurial  gasometer.  But 
above  the  disc  which  terminates  this  column  at  the  upper  end, 
is  fixed  a  new  joint,  which  allows  the  horizontally-balanced 
tube  at  the  end  of  which  the  artificial  insect  is  placed,  to 
oscillate  in  the  vertical  plane  like  a  scale-beam.  In  order  to 
establish  a  communication  between  the  revolving  column  and 
the  tube  carrying  the  insect,  we  make  use  of  a  little  india- 
rubber  tube,  sufficiently  flexible  not  to  interfere  with  the 
oscillatory  movements  of  the  apparatus. 

Other  accessory  modifications  may  be  seen  in  fig.  88  ;  one 
consists  in  employing  a  glass  tube  to  convey  the  air  from  the 
pump  which  moves  the  insect ;  the  other  in  a  change  of  the 
mechanism  by  which  motion  is  imparted  to  the  wings.  The 
most  important  alteration  is  the  introduction  of  a  joint  which 
allows  us  to  give  every  possible  inclination  to  the  plane  in 
which  the  wings  oscillate. 

The  apparatus  being  arranged  so  that  the  counterpoise, 
having  been  brought  nearer  to  the  point  of  suspension,  does 
not  exactly  balance  the  weight  of  the  insect,  the  latter  is 


MECHANISM  OF  INSECT  FLIGHT. 


207 


placed  so  that  its  wings  may  move  in  a  horizontal  plane,  the 
main-rib  being  uppermost.  Thus  all  the  motive  force  is 
directed  from  below  upwards,  and  as  soon  as  the  pump  begins 
to  act,  we  see  the  insect  rise  vertically.  We  can  easily  esti- 
mate the  weight  raised  by  the  flapping  of  the  wings,  and  as 
we  can  vary  the  weight  of  the  insect  by  altering  the  position 
of  the  counterpoise,  we  can  determine  the  effort  which  is 
developed  according  to  the  frequency  or  the  amplitude  of  the 
strokes. 

By  turning  the  insect  half  way  round,  so  that  its  wings, 
still  oscillating  in  a  horizontal  plane,  should  turn  their  main- 
rib  downwards,  we  develop  a  descending  vertical  force  which 
may  be  measured  by  removing  the  counterpoise  to  a  greater 
or  less  distance,  and  causing  it  to  be  raised  by  the  descent  of 
the  insect. 

If  we  adjust  the  plane  of  oscillation  of  the  wings  vertically, 
the  insect  turns  horizontally  round  its  point  of  support  in 
the  same  manner  as  has  been  previously  described  and 
represented  in  fig.  87. 

Lastly,  if  we  give  to  the  plane  of  oscillation  of  the  wings, 
the  oblique  position  which  it  presents  in  the  greater  number 
of  insects ;  that  is  to  say,  so  that  the  main-rib  turns  at  once 
upwards  and  slightly  forward,  we  see  the  insect  rise  against 
its  own  weight,  and  turn  at  the  same  time  round  the  vertical 
axis  ;  in  a  word,  the  apparatus  represents  the  double  effect 
which  is  observed  in  a  flying  insect,  which  obtains  from  the 
stroke  of  its  wings,  both  the  force  which  sustains  it  in  the 
air,  and  that  which  directs  its  course  in  space. 

The  first  of  these  forces  is  by  far  the  more  considerable ; 
thus,  when  an  insect  hovers  over  a  flower,  and  we  see  it 
illuminated  obliquely  by  the  setting  sun,  we  may  satisfy  our- 
selves that  the  plane  of  oscillation  of  its  wings  is  nearly  hori- 
zontal. This  inclination  must  evidently  be  modified  as  soon 
as  the  insect  wishes  to  dart  off  rapidly  in  any  direction,  but 
then  the  eye  can  scarcely  follow  it,  and  detect  the  change  of 
plane,  the  existence  of  which  we  are  compelled  to  admit  by 
the  theory  and  the  experiments  already  detailed. 

A  curious  point  of  study  would  be  the  movements  prepara- 


208 


ANIMAL  MECHANISM. 


tory  to  flight.  We  speak  not  only  of  the  spreading  of  the 
wings,  which  in  the  coleoptera  precedes  flight,  a  movement 
which  is  sometimes  so  slow  as  to  be  easily  observed,  nor  of 
the  unfolding  of  the  first  pair  of  wings,  as  wasps  do  before 
they  fly.  Other  insects,  the  diptera,  turn  their  wings  as  on 
a  pivot  around  its  main-rib  in  a  very  remarkable  manner, 
at  the  moment  when  the  wings  which  were  previously  ex- 
tended on  the  back  in  the  attitude  of  repose  start  outwards 
and  forwards  before  they  begin  to  fly.  Flies,  tipulge  and 
many  other  kinds,  show  this  preparatory  movement  very  clearly 
when  the  insect,  being  exhausted,  has  no  longer  any  energy 
in  its  flight.  We  see  the  main-rib  of  the  wing  remain  sen- 
sibly immovable,  and  around  it  turns  the  membranous  portion 
whose  free  border  is  directed  downwards.  This  position 
having  been  obtained,  the  insect  has  only  to  cause  its  wing 
to  oscillate  in  an  almost  horizontal  direction  from  backwards 
forwards,  and  from  forwards  backwards.  If  this  motion  as  on 
a  pivot  did  not  exist,  the  wing  would  cut  the  air  with  its  edge, 
and  would  be  utterly  incapable  of  producing  flight.  In  other 
species,  as  in  the  agrion,  a  small  dragon-fly,  for  instance,  the 
four  wings,  during  repose,  are  laid  back  to  back  one  against 
the  other  above  the  abdomen  of  the  animal.  Their  main- 
ribs  are  upwards,  and  keep  their  position  when  the  wings  pass 
downwards  and  forwards ;  here  no  preparation  for  flight  is 
necessary,  In  these  insects,  as  in  butterflies,  the  wing  has 
only  to  set  itself  in  motion  when  the  creature  flies. 

It  is  interesting  to  follow  throughout  the  series  of  insects 
the  variations  presented  by  the  mechanism  of  flight. 

The  confirmation  of  the  theory  just  propounded  is  found  in 
the  experiments  which  certain  naturalists  have  made  by 
means  of  vivisection.  For  the  most  interesting  of  these  we 
are  indebted  to  Professor  M.  Giraud.  All  these  experiments 
prove  that  the  insect  needs  for  the  due  function  of  flight  a 
rigid  main-rib  and  a  flexible  membrane.  If  we  cover  the 
flexible  part  of  the  wing  with  a  coating  which  hardens  as  it 
dries,  flight  is  prevented.  We  hinder  it  also  by  destroying 
the  rigidity  of  the  anterior  nervuie. 

If  we  only  cut  off,  on  the  contrary,  a  portion  of  the  flexible 
membrane,  parallel  to  its  hinder  edge,  the  power  of  flight 


THE   FLIGHT  OF  WKDS. 


209 


is  preserved,  for  the  wing  retains  the  conditions  essential  to 
this  function — namely,  a  rigid  main-rib  and  a  flexible  sur- 
face. Lastly,  in  some  species  the  combination  of  two  wings 
is  indispensable  to  flight;  a  kind  of  pseudo-elytron  consti- 
tutes the  nervure,  and  behind  this  is  extended  a  membranous 
wing,  which  is  locked  in  with  the  posterior  border  of  the 
anterior  one.  This  second  wing  does  not  present  sufficient 
rigidity  to  enable  it  to  strike  the  air  with  advantage,  and  in 
these  insects  flight  is  rendered  impossible,  if  we  cut  off  the 
false  wing-case ;  it  is  as  if  we  had  destroyed  the  main-rib  of 
a  perfect  wing. 


CHAPTER  III. 
OF  THE  FLIGHT  OF  BIRDS. 

Conformation  of  the  bird  with  reference  to  flight— Structure  of  the  wing, 
its  curves,  its  muscular  apparatus — Muscular  force  of  the  bird  ; 
rapidity  of  contraction  of  its  muscles— Form  of  the  bird  ;  stable 
equilibrium  ;  conditions  favourable  to  cbange  of  plane  —  Proportion  of 
the  surface  of  the  wings  to  the  weight  of  the  body  in  birds  of  different 
size. 

The  plan  by  which  we  have  been  guided  in  the  study  of 
insect  flight  must  also  be  followed  in  investigating  that  of 
birds.  It  will  be  necessary  to  determine,  by  a  delicate  mode 
of  analysis,  the  movements  produced  by  the  wing  during 
flight ;  from  these  movements  we  may  draw  a  conclusion  as 
to  the  resistance  of  the  air  which  affords  the  bird  a  fulcrum 
on  which  to  exert  its  force.  Then,  having  propounded  cer- 
tain theories  respecting  the  mechanism  of  flight,  the  force 
required  for  the  work  effected  by  the  bird,  &c,  we  will  under- 
take to  represent  these  phenomena  by  means  of  artificial 
instruments,  as  we  have  already  done  with  respect  to  insects. 

But,  before  we  enter  methodically  on  this  study,  it  will  be 
useful  to  prepare  ourselves  for  it  by  some  general  observa- 
tions on  the  organization  of  the  bird,  the  structure  of  its  wings, 
the  force  of  its  muscular  system,  its  conditions  of  equilibrium 
in  the  air.  &c 
20 


210 


ANIMAL  MECHANISM. 


Conformation  of  the  bird. —  By  the  simple  inspection  of  a 
bird's  wing,  it  is  easy  to  see  that  the  mechanism  of  its  flight 
is  altogether  different  from  that  of  an  insect.  From  the 
manner  in  which  the  feathers  of  its  wing  lie  upon  each  other, 
it  is  evident  that  the  resistance  of  the  air  can  only  act  from 
below  upwards,  for  in  the  opposite  direction  the  air  would 
force  for  itself  an  easy  passage  by  bending  the  long  barbs  of 
the  feathers,  which  would  no  longer  sustain  each  other.  This 
well-known  arrangement,  so  carefully  described  by  Prechlt,* 
has  caused  persons  to  suppose  that  the  wing  only  needed  to 
oscillate  in  a  vertical  plane  .in  order  to  sustain  the  weight  of 
the  bird,  because  the  resistance  of  the  air  acting  from  be- 
low upwards  is  greater  than  that  which  it  exerts  in  the 
opposite  direction. 

This  writer  has  been  wrong  in  basing  on  the  inspection  of 
the  organ  of  flight  all  the  theory  of  its  function.  We  shall  find 
that  experiment  contradicts  in  the  most  decided  manner  these 
premature  inductions. 

If  we  take  a  dead  bird,  and  spread  out  its  wings  so  as  to 
place  them  in  the  position  represented  in  tig.  89,  we  see  that  at 


Fig.  89.— Various  curves  of  the  wing  of  a  bird  at  different  points  in  its 
length. 


different  points  in  its  length,  the  wing  presents  very  remark- 
able changes  of  plane.  At  the  inner  part,  towards  the  body, 
the  wing  inclines  considerably  both  downwards  and  back- 
wards, while  near  its  extremity,  it  is  horizontal  and  some- 
times slightly  turned  up,  so  that  its  under  surface  is  directed 
somewhat  backward. 

Dr.  Pettigrew  thought  that  he  could  find  in  this  curve  a 
surface  resembling  a  left-handed  screw  propeller ;  struck  with 
the  resemblance  between  the  form  of  the  wing  and  that  of 
the  screw  used  in  navigation,  he  considered  the  wing  of  a 

*  Untersuchungen  iiber  den  Flug  der  Vogel.    8vo.    Vienna  :  1846. 


THE  FLIGHT  OF  BIRDS. 


211 


bird  as  a  screw  of  which  the  air  formed  the  nut.  We  do 
not  think  that  we  need  refute  such  a  theory.  It  is  too  evi- 
dent that  the  alternating  type  which  belongs  to  every  muscular 
movement  cannot  tend  to  produce  the  propulsive  action  of  a 
screw ;  for  while  we  admit  that  the  wing  revolves  on  an  axis, 
this  rotation  is  confined  to  the  fraction  of  a  turn,  and  is  fol- 
lowed by  rotation  in  the  opposite  direction,  which  in  a  screw 
would  entirely  destroy  the  effect  produced  by  the  previous 
movement.  And  yet  the  English  writer  to  whose  ideas  we 
refer  has  been  so  fully  convinced  of  the  truth  of  his  theory 
that  he  has  wished  to  extend  it  to  the  whole  animal  kingdom. 
He  proposes  to  refer  locomotion  in  all  its  forms,  whether 
terrestrial,  aquatic,  or  aerial  to  the  movements  of  a  screw 
propeller.  Let  us  only  seek  in  the  anatomical  structure  of 
the  organs  of  flight  the  information  which  it  can  afford  us  ; 
that  is  to  say,  that  which  refers  to  the  forces  which  the  bird 
can  develop  in  flight,  and  the  direction  in  which  these  forces 
are  exerted. 

Comparative  anatomy  shows  us  in  the  wing  of  birds  an 
analogue  of  the  fore  limb  of  mammals.  The  wing  when 
reduced  to  its  skeleton,  presents,  as  in  the  human  arm,  the 
humerus,  the  two  bones  of  the  fore-arm,  and  a  rudimentary 
hand,  in  which  we  still  find  metacarpal  bones  and  phalanges. 
The  muscles  also  present  many  analogies  with  those  of  the 
anterior  limb  of  man  ;  some  parts  of  these  bear  such  a  resem- 
blance both  in  appearance  and  in  function,  that  they  have 
been  designated  by  the  same  name. 

In  the  wring  of  the  bird,  the  most  strongly  developed  muscles 
are  those  whose  office  it  is  to  extend  or  bend  the  hand  upon 
the  fore-arm,  the  fore-arm  on  the  humerus,  and  also  to  move 
the  humerus,  that  is  say,  the  whole  arm,  round  the  articula- 
tion of  the  shoulder. 

In  the  greater  number  of  birds,  especially  of  the  larger 
kinds,  the  wing  seems  to  remain  always  extended  during  flight. 
Thus,  the  extensor  muscles  of  the  different  portions  of  this 
organ  would  serve  to  give  this  organ  the  position  necessary 
for  rendering  flight  possible,  and  for  maintaining  it  in  this  posi- 
tion ;  as  to  motive  work,  it  would  be  executed  by  other  muscles, 
much  stronger  than  the  preceding — namely,  the  pectorals. 


212 


ANIMAL  MECHANISM. 


All  the  anterior  surface  of  the  thorax  of  birds  is  occupied 
by  powerful  muscular  masses,  and  especially  by  a  large 
muscle,  which  by  its  attachments  to  the  sternum,  to  the  ribs 
and  the  humerus,  is  analogous  with  the  large  pectoral  muscle 
in  man  and  the  mammals ;  its  office  is  evidently  to  lower  the 
wing  with  force  and  rapidity,  and  thus  to  gain  from  the  air 
the  fulcrum  necessary  to  sustain,  as  well  as  to  move  the  mass 
of  the  body.  Underneath  the  large  pectoral  is  found  the 
medium,  pectoral,  whose  action  is  to  raise  the  wing.  On  the 
exterior,  the  small  pectoral,  acting  as  accessory  to  the  large 
one,  extends  from  the  sternum  to  the  humerus. 

Since  the  force  of  a  muscle  is  in  proportion  to  the  volume 
of  this  organ,  when  we  consider  that  these  pectoral  muscles 
represent  about  one- sixth  part  of  the  whole  weight  of  the 
bird,  we  shall  immediately  understand  that  the  principal 
function  of  flight  devolves  on  these  powerful  organs. 

Borelli  endeavoured  to  deduce  from  the  volume  of  the  pec- 
toral muscles  the  energy  of  which  they  are  capable;  he  con- 
cluded that  the  force  employed  by  the  bird  in  flight  was  equal 
to  10,000  times  its  weight.  We  will  not  here  refute  the 
error  of  Borelli ;  many  others  have  undertaken  to  combat  his 
notions,  and  have  substituted  for  the  calculations  of  the  Italian 
physiologist  others  whose  correctness  it  would  be  difficult  to 
prove.  Such  great  contradictions  as  are  to  be  found  in  the 
different  estimates  formed  of  the  muscular  force  of  birds  have 
arisen  from  the  fact  that  these  attempts  at  measurement  were 
premature. 

Navier,  depending  on  calculations  which  were  not  based  on 
experiment,  considered  himself  authorized  in  admitting  that 
birds  develop  enormous  mechanical  work :  seventeen  swallows 
would  exert  work  equal  to  a  horse  power.  "  As  easy  would  it 
be,"  said  M.  Bertrand,  facetiously,  "  to  prove  by  calculation 
that  birds  could  not  fly — a  conclusion  which  would  rather  com- 
promise mathematics." 

Besides,  we  find  that  Cagniard  Latour  admitted,  basing  his 
assertion  on  theory,  that  the  wing  is  lowered  eight  times  more 
quickly  than  it  rises.  Experiment,  however,  proves  that  the 
wing  of  the  bird  is  raised  more  quickly  than  it  descends. 

Estimate  of  the  muscular  force  of  the  bird. — We  must  at  the 


FORCE  OF  BIRDS. 


213 


present  day  measure  mechanical  force  under  the  form  of  work. 
It  is  necessary  for  this  purpose  to  know  what  resistance  is 
met  with  by  the  wing  at  each  instant  of  its  movements, 
and  the  direction  in  which  it  repels  from  it  this  resisting 
medium. 

Such  an  estimate  requires  a  previous  knowledge  of  the 
resistance  of  air  against  surfaces  of  different  curvature  moving 
with  various  degrees  of  velocity ;  it  supposes  at  the  same  time 
that  we  know  the  movements  of  the  wing  as  well  as  their 
velocity  and  direction  at  every  instant. 

This  problem  will  perhaps  be  the  last  which  we  may  hope 
to  solve,  but  we  may  even  now  study  from  other  points  of 
view  the  force  exerted  by  the  muscles  of  the  bird,  and  esti- 
mate some  of  its  characteristics. 

Thus,  we  may  obtain  experimentally  a  measure  of  the  maxi- 
mum effort  which  these  muscles  can  exert.  This  measure  may 
not  really  correspond  with  the  real  effort  displayed  in  flight, 
but  it  may  keep  us  from  forming  exaggerated  estimates. 

If  the  calculations  of  Borelli,  or  even  those  of  Navier  were 
correct,  we  ought  to  find  in  the  muscles  of  the  bird  a  very 
considerable  statical  force.  Experiments  show,  however,  that 
these  muscles  do  not  seem  capable  of  more  energetic  efforts 
than  those  of  other  animals. 

Experiment. — Our  first  experiment  was  made  upon  a  buz- 
zard. The  creature  being  hoodwinked  was  stretched  upon  its 
back,  with  its  wings  held  on  the  table  by  bags  filled  witli 
small  shot.  The  application  of  the  hood  plunges  these  birds 
into  a  sort  of  hypn^ijsnij  during  which  we  can  make  any  num- 
ber of  experiments  upon  them,  without  their  evincing  any  pain. 

We  laid  bare  the  great  pectoral  muscle  and  the  humeral 
region,  we  placed  a  ligature  on  the  artery,  disarticulated  the 
elbow-joint,  and  took  away  all  the  rest  of  the  wing.  A  cord 
was  fixed  to  the  extremity  of  the  humerus,  and  at  the  end  of 
this  cord  was  placed  a  scale-pan,  into  which  small  shot  was 
poured.  The  trunk  of  the  bird  being  rendered  perfectly  im- 
movable, we  excited  the  muscle  by  means  of  interrupted  in- 
duced currents ;  while  the  artificial  contraction  was  produced, 
an  assistant  poured  into  the  pan  the  small  shot,  until  the 
force  of  contraction  of  the  muscle  was  counteracted.    At  this 


214 


ANIMAL  MECHANISM. 


movement,  the  weight  supported  was  2  kilogrammes  380 
grammes  (about  6*38  lbs.  troy). 

If  we  take  into  account  the  unequal  length  of  the  arms  of 
the  lever,  on  the  side  of  the  power  and  that  of  the  resistance, 
we  find  that  the  pectoral  muscle  had  been  able  to  produce  a 
total  effort  of  12  kilogrammes  600  grammes  (about  33  78  lbs. 
troy),  which  would  correspond  with  a  traction  of  1298 
grammes  (3  66  lbs.  troy)  for  each  square  centimetre  of  the 
transverse  section  of  the  muscle. 

A  pigeoD  placed  under  the  same  conditions  has  given,  as  its 
entire  effort,  a  weight  of  4860  grammes,  which,  according  to 
the  transverse  section  of  its  muscle,  raised  to  1400  grammes 
the  effort  which  each  muscular  bundle  could  develop  for  every 
square  centimetre  of  section. 

If  we  admit  that  the  electrical  action  employed  in  these 
experiments  to  make  the  muscles  contract,  develops  an  effort 
less  than  that  which  is  caused  by  the  will,  it  is  not  less  true 
that  these  estimates,  which  are  less  than  those  which  we 
generally  obtain  in  the  muscles  of  mammals  under  the  same 
conditions,  do  not  authorize  us  in  recognizing  in  the  bird  any 
special  muscular  power. 

Lastly,  if  we  were  to  take  into  account  in  this  estimate 
the  laws  of  thermo -dynamics,  we  might  affirm  that  the  bird 
would  not  develop  in  flight  a  very  especial  amount  of  work. 

All  work,  in  fact,  can  only  be  performed  with  a  certain 
waste  of  substance,  and  if  the  act  of  flying  involved  a  great 
expenditure  of  work,  we  ought  to  find  a  notable  diminution 
of  weight  in  a  bird  when  it  returns  from  a  long  flight.  Nothing 
of  this  kind  is  observed.  Persons  who  train  carrier  pigeons 
have  given  us  information  on  this  point,  from  which  we  gather 
that  a  bird  which  has  traversed  in  a  single  flight  a  distance  ot 
fifty  leagues  (which  it  seems  to  do  without  taking  any  food), 
weighs  only  a  few  grammes  less  than  at  its  departure.  It 
would  be  interesting  to  make  these  experiments  again  with 
greater  exactitude. 

Of  the  rapidity  of  the  muscular  actions  of  birds. — One  of  the 
most  striking  peculiarities  in  the  action  of  a  bird's  muscles 
is  the  extreme  rapidity  with  which  force  is  engendered  in 
them.  Among  the  different  species  of  animals  whose  muscular 


RAPIDITY  OF  BIRDS. 


215 


acts  we  have  determined,  the  bird  is  that  which,  after  the 
insect,  has  given  the  most  rapid  movements. 

This  rapidity  is  indispensable  to  flight.  In  fact,  the  wing 
when  lowered,  can  meet  with  a  sufficient  resistance  in  the 
air  only  when  it  moves  with  great  velocity.  The  resistance 
of  the  air  against  a  plane  surface  which  strikes  upon  it 
and  repels  it,  evidently  increases  in  the  ratio  of  the  square 
of  the  velocity  with  which  this  plane  is  displaced.  It 
would  be  of  no  use  for  the  bird  to  have  energetic  muscles, 
capable  of  effecting  considerable  work,  if  they  could  only 
give  slow  movements  to  the  wing;  their  force  could  not 
be  exerted  for  want  of  resistance,  and  no  work  could  be  pro- 
duced. It  is  otherwise  with  terrestrial  animals  which  run  or 
creep  on  the  ground,  with  a  speed  more  or  less  rapid  accord- 
ing to  the  nature  of  their  muscles,  but  which  in  every  case 
utilize  their  muscular  force  by  means  of  the  perfect  resistance 
of  the  ground.  The  necessity  of  velocity  in  the  movements 
of  fishes  has  been  already  observed,  since  the  water  in  which 
they  swim  resists  more  or  less,  according  to  the  rapidity 
with  which  their  tails  or  their  fins  act  upon  it.  Thus  the 
muscular  action  of  fishes  is  rapid,  but  much  less  so  than 
that  of  birds,  which  move  in  a  medium  far  more  yielding. 

In  order  to  understand  the  rapid  production  of  movements 
in  the  muscles  of  the  bird,  we  must  remember  that  these 
movements  are  connected  with  chemical  action,  produced  in 
the  very  substance  of  the  muscle,  where  they  give  rise,  as  ia 
machines,  to  heat  and  motion.  We  must  therefore  admit 
that  these  actions  are  excited  and  propagated  more  readily 
in  the  muscles  of  birds  than  in  those  of  any  other  species  of 
animals.  In  the  same  maimer  the  different  kinds  of  powder 
used  in  war  differ  much  from  each  other  in  the  rapidity  of 
their  explosion,  and  consequently  give  very  different  velocities 
to  the  projectiles  which  they  impel. 

Lastly,  the  form  of  movement  presents  in  different  species 
of  birds  peculiarities  which  wre  have  already  noticed.  We 
have  seen  in  Chapter  VIII.  how  much  the  dimensions  of  the 
pectoral  muscles  vary  according  as  the  strokes  of  the  wing  are 
required  to  have  much  force  or  great  extent ;  therefore  wo 
shall  not  recur  again  to  this  subject. 


216 


ANIMAL  MECHANISM. 


Form  of  the  bird. — All  those  who  have  studied  the  flight  of 
birds  have  very  properly  paid  great  attention  to  the  form  of 
these  creatures,  as  rendering  them  eminently  adapted  to  flight. 
They  have  recognised  in  them  perfect  stable  equilibrium  in 
the  aerial  medium.  They  have  thoroughly  understood  the 
part  played  by  the  large  surfaces  formed  by  the  wings,  which 
may  sometimes  act  as  a  parachute,  to  produce  a  very  slow 
descent ;  while  at  other  times  these  surfaces  glide  through  the 
air,  and  following  the  inclination  of  their  plane,  allow  the 
bird  to  descend  very  obliquely,  and  even  to  rise,  or  to  hover 
while  keeping  its  wings  immovable.  Some  observers  have 
gone  so  far  as  to  admit  that  certain  species  of  birds  play 
an  entirely  passive  part  in  flight,  and  that  giving  up  their 
wings  to  the  impulse  of  the  wind,  they  derive  from  it  a  force 
capable  of  carrying  them  in  every  direction,  even  against  the 
wind.  It  seems  to  us  interesting  to  discuss,  in  a  few  words, 
this  important  question  in  the  theory  of  flight. 

The  stable  equilibrium  of  the  bird  has  been  well  explained  ; 
there  is  nothing  for  us  to  add  to  the  remarks  which  have  been 
made  on  this  subject.  The  wings  are  attached  exactly  at 
the  highest  part  of  the  thorax,  and  consequently  when  the 
outstretched  wings  act  upon  the  air  as  a  fulcrum,  all  the 
weight  of  the  body  is  placed  below  this  surface  of  suspension. 
We  know  also  that  in  the  body  itself,  the  lightest  organs,  the 
lungs  and  the  air  vessels,  are  in  the  upper  part;  while 
the  mass  of  the  intestines,  which  is  heavier,  is  lower ;  also 
that  the  thoracic  muscles,  which  are  so  voluminous  and  heavy, 
occupy  the  lower  part  of  the  system.  Thus  the  heaviest 
part  js*  placed  as  low  as  possible  beneath  the  point  of  sus- 
pension. 

The  bird,  as  it  descends  with  its  wings  outspread,  will  thus 
present  its  ventral  region  downwards,  without  its  being  neces- 
sary to  make  an  effort  to  keep  its  equilibrium ;  it  will  take 
this  position  passively,  like  a  parachute  set  free  in  space,  or 
like  the  shuttlecock  when  it  falls  upon  the  battledore. 

But  this  vertical  descent  is  an  exceptional  case ;  the  bird 
which  allows  itself  to  fall  is  almost  always  impelled  by  some 
previous  horizontal  velocity;  it  therefore  slides  obliquely  upon 
the  air,  as  every  light  body  of  large  surface  does  when  phiced 


FORM  OF  THE  BIRD. 


217 


under  the  conditions  of  stable  equilibrium  which  we  have 
just  described.  Mons.  J.  Pline  has  carefully  studied  the 
different  kruds  of  sliding  movement  which  may  take  place ;  he 
has  even  represented  them  by  means  of  small  pieces  of  appa- 
ratus which  imitate  the  insect  or  the  bird  when  they  fly 
without  moving  their  wings. 

If  we  take  a  piece  of  paper  of  a  square  form,  and  fold  it  in 

I  / 

h®  1  #-  — ©  7 


H©  1  <©-  -o- 


Hi  '  ®- 

Fio.  90. — Representing,  on  the  left,  a  contrivance  intended  to  imitate  the 
hovering  of  birds;  it  is  placed  in  equilibrium  by  two  equal  weights 
attached  to  the  extremities  of  a  wire  which  is  fixed  in  the  lower  part  of 
the  angle  formed  by  the  folded  paper.  This  piece  of  apparatus  ("alls  verti- 
cally, as  shown  by  the  successive  positions  of  the  wire  when  attached  to 
the  two  weights.  On  the  right  is  seen  the  same  contrivance  connected 
with  one  weight  only.  Its  fall  is  parabolic,  as  thown  by  the  dotted 
trajectory. 

the  middle,  so  as  to  form  a  very  obtuse  aDgle  (fig.  90) ;  then, 
at  the  bottom  of  this  angle,  let  us  fix  with  a  little  wax  a 
piece  of  wire  attached  to  two  masses  of  the  same  weight ;  we 
shall  have  a  system  which  will  maintain  stable  equilibrium 
in  the  air.  If  the  centre  of  gravity  pass  exactly  through  the 
centre  of  the  figure,  we  shall  see  it  descend  vertically  when 
we  let  it  go,  the  convexity  of  its  angle  beiDg  directed  down- 
wards. 

If  we  take  away  one  of  the  weights,  so  as  to  alter  the 
position  of  the  centre  of  gravity,  the  apparatus,  instead  of 
descending  vertically,  will  follow  an  oblique  trajectory,  and 
will  glide  through  the  air  with  an  accelerated  motion  (fig.  90, 
to  the  right). 


218 


ANIMAL  MECHANISM. 


The  trajectory  passed  through  by  this  little  instrument  will 
be  situated  in  a  vertical  plane,  if  the  two  halves  of  the  appa- 
ratus are  perfectly  symmetrical;  but  if  they  are  not,  it  will 
turn  towards  the  side  in  which  while  it  cuts  the  air  it  finds 
the  greater  resistance.  These  effects,  which  are  easily  un- 
derstood, are  identical  with  those  which  the  resistance  of  the 
rudder  causes  in  the  advancing  motion  of  a  ship.  They  can 
also  be  produced  in  a  vertical  direction  ;  so  that  the  trajectory 
of  the  apparatus  may  be  a  curve  with  its  concavity  above  or 
below,  as  the  case  may  be. 

Every  thin  body  which  is  curved  tends  to  glide  upon  the 
air  according  to  the  direction  of  its  own  curvature. 


Fig  91. — We  have  turned  back  the  riaht  hand  corner  of  the  two  planes 
which  form  the  angle.  After  a  descent  in  a  parabolic  curve,  the  apparatus 
rises  again,  as  shown  by  the  dotted  trajectory. 

If  we  turn  back  either  the  anterior  or  posterior  edge  of  our 
little  apparatus,  we  shall  see  it  at  a  given  moment  of  its 
descent  rise  in  opposition  to  its  own  weight,  but  it  will  soon 
lose  its  upward  movement  (fig.  91).  Let  us  consider  what 
has  taken  place. 

So  long  as  the  paper  descended  with  but  slight  rapidity, 
the  effect  of  its  curvature  was  not  perceptible,  because  the 
air  resists  surfaces  only  in  the  ratio  of  the  velocity  with  which 
they  move.     But  when  the  rapidity  was  sufficiently  great,  an 


FORM  OF  THE  IilKD. 


219 


effect  was  produced  similar  to  that  of  a  rudder,  which  turned 
up  the  anterior  extremity  of  the  little  apparatus,  and  gave  it 
an  ascending  course.  Immediately,  the  weight  which  was 
the  generating  force  of  its  gliding  movement  through  the  air 
began  to  retard  it ;  in  proportion  as  it  rose,  it  lost  its  velo- 
city until  it  reached  the  point  of  rest.  After  that,  a  downward 
movement  commenced,  then  an  ascent  in  the  opposite  direc- 
tion, so  that  the  paper  descended  to  the  ground  by  successive 
oscillations. 

If  we  give  the  apparatus  a  slight  concavity  downwards, 
the  opposite  effect  is  produced;  we  see  (fig.  92),  at  a  certain 


Fig.  92.— The  right  hand  corner  of  the  pLine  of  the  angle  has  been  bent 
downwards.  After  a  parabolic  desceut,  the  apparatus  falls  very  rapidly 
in  a  perpendicular  direction. 


moment,  the  trajectory  turns  abruptly  downwards,  and  the 
falling  body  strikes  the  ground  with  considerable  violence.  In 
this  second  case,  when  the  rudder-like  effect  is  produced,  the 
new  direction  has  in  its  favour  the  weight  which  hastens  the 
fall  of  the  little  instrument,  as  in  the  former  experiment  it 
rendered  the  re- ascent  more  slow. 

We  have  dwelt  upon  these  effects,  because  they  often  occur 
in  the  flight  of  birds.  They  are  mentioned  in  the  old  treatises 
on  falconry,  which  describe  the  evolutions  of  birds  used  in 


220 


ANIMAL  MECHANISM. 


hawking.  Without  going  further  back,  we  find  in  Huber*  the 
description  of  these  curvilinear  movements  of  falcons,  to  which 
they  gave  the  name  of  passades,  and  which  consisted  of  an 
oblique  descent  of  the  bird,  followed  by  a  re-ascent,  which 
they  called  ressource  (from  the  Latin,  resurgere).  "  The  bird," 
says  Huber,  "  carried  forward  by  its  own  velocity,  would  dash 
itself  against  the  ground,  were  it  not  that  it  exercises  a  cer- 
tain power  which  it  possesses  of  stopping  when  at  its  utmost 
speed,  and  turning  directly  upwards  to  a  sufficient  height  to 
enable  it  to  make  a  second  descent.  This  movement  is  able 
not  only  to  arrest  its  descent,  but  also  to  carry  it  without  any 
further  effort,  as  high  as  the  level  from  which  it  started." 

Surely,  there  is  some  exaggeration  in  saying  that  the  bird 
can  rise,  without  any  active  effort,  to  the  height  from  which 
it  stooped ;  the  resistance  of  the  air  must  destroy  a  portion  of 
the  force  which  it  had  acquired  during  its  descent,  and  which 
must  be  transformed  into  a  rising  impulse.  We  see,  how- 
ever, that  the  phenomenon  of  the  ressource  has  been  noticed 
by  many  observers,  and  that  it  has  been  considered  by  them 
as,  to  a  certain  extent,  a  passive  motion  in  which  the  bird 
has  to  employ  no  muscular  force. 

The  act  of  hovering  presents,  in  certain  cases,  a  great  ana- 
logy with  the  phenomena  just  described.  When  a  bird — a 
pigeon,  for  example — has  traversed  a  certain  distance  by  flap- 
ping its  wings,  we  see  it  suspend  all  these  movements  for 
some  instants,  and  glide  on  either  horizontally,  ascending  or 
descending.  The  latter  kind  of  hovering  motion  is  that  which 
is  of  longest  duration ;  in  fact,  it  is  only  an  extremely  slow 
fall,  but  in  which  the  weight  assists  the  movement,  while 
it  checks  it  in  the  horizontal  or  ascending  course.  In  the  last 
two  forms,  the  wing,  directed  more  or  less  obliquely,  derives 
its  point  of  resistance  from  the  air,  like  the  child's  plaything 
called  a  kite,  but  with  this  difference,  that  the  velocity  is 
given  to  the  kite  by  the  tractile  force  exerted  on  the  string 
when  the  air  is  calm,  while  the  bird  when  it  hovers  utilizes 
the  speed  which  it  has  already  acquired,  either  by  its  oblique 
fall  or  by  the  previous  flapping  of  its  wings. 

We  have  already  said,  that  observers  had  admitted  that 

*  8vo.  Geneva,  1784. 


FORM  OF  THE  151  RD. 


221 


certain  birds  which  they  called  "sailing  birds"  could  sustain 
and  direct  themselves  in  the  air  solely  by  the  action  of  the 
wind.  This  theory  has  all  the  appearance  of  a  paradox  ;  we 
cannot  understand  how  the  bird,  when  in  the  wind,  and  using 
no  exertion,  should  not  be  affected  by  its  force. 

If  the  passades,  or  the  changes  which  it  effects  in  the  plane 
of  its  wings,  can  sometimes  carry  it  in  a  direction  con- 
trary to  that  of  the  wind,  these  can  be  only  transient  effects, 
compensated  afterwards  by  a  greater  force  driving  them 
before  the  wind. 

Nevertheless,  this  theory  of  sailing  flight  has  been  advo- 
cated with  great  talent  by  certain  observers,  and  especially  by 
Count  d'Esterno,  the  author  of  a  remarkable  memoir  on  the 
flight  of  birds. 

"Everyone,"  says  this  author,  "must  have. seen  certain 
birds  practise  this  kind  of  sailing  flight;  to  deny  it,  is  to 
contradict  evidence." 

We  know  so  little  yet  of  the  resistance  of  the  air,  especially 
with  reference  to  the  resolution  of  this  force  when  it  acts 
against  inclined  planes  under  different  angles,  that  it  is  im- 
possible to  decide  on  this  question  as  to  sailing  flight.  It 
would  be  rash  absolutely  to  condemn  the  opinion  of  observers, 
by  depending  on  a  theory  or  on  notions  as  vague  as  those 
which  we  possess  on  this  subject. 

Ratio  of  the  surface  of  the  wings  to  the  weight  of  the  body.— 
One  of  the  most  interesting  points  in  the  conformation  of  birds 
consists  in  the  determination  of  the  ratio  borne  by  the  surface 
of  the  wings  to  the  weight  of  the  bird.  Is  there  a  constant 
relation  between  these  two  quantities  ?  This  question  has 
been  the  cause  of  many  controversies. 

It  has  already  been  shown  that,  if  we  compare  birds  of 
different  species  and  of  equal  weight,  we  may  find  that  some 
have  their  wings  two,  three,  or  four  times  more  extended 
than  the  others.  The  birds  with  large  wing  surfaces  are 
those  which  usually  give  themselves  up  to  a  kind  of  hovering 
flight,  and  have  been  called  sailing  birds;  while  those  whose 
wing  is  short  or  narrow  are  more  usually  accustomed  to  a 
flight  which  resembles  rowing.  If  we  compare  together 
two  "rowing"  or  two  "sailing"  birds;  if,  to  be  more 
21 


222 


ANIMAL  MECHANISM. 


exact,  we  choose  them  from  the  same  family .  ia  order  to  have 
no  difference  between  them  except  that  of  size,  we  shall  find 
a  tolerably  constant  ratio  between  the  weight  of  these  birds 
and  the  surface  of  their  wings.  But  the  determination  of  this 
ratio  must  be  based  upon  certain  considerations  which  have 
been  long  disregarded  by  naturalists. 

Mons.  de  Lucy  has  endeavoured  to  compare  the  surface  of 
the  wings  with  the  weight  of  the  body  in  all  flying  animals. 
Then,  in  order  to  establish  a  common  unit  between  creatures 
of  such  different  species  and  size,  he  referred  all  these  esti- 
mates to  an  ideal  type,  the  weight  of  which  was  always  one 
kilogramme.  Thus,  having  ascertained  that  the  gnat,  which 
weighs  three  milligrammes,  possesses  wings  of  thirty  square 
millimetres  of  surface,  he  concluded  that  in  the  gnat  type 
each  kilogramme  of  the  animal  was  supported  by  an  alar  sur- 
face of  ten  square  millimetres. 

Having  drawn  up  a  comparative  table  of  measurements 
taken  in  animals  of  a  great  number  of  different  species 
and  sizes,  Mons.  de  Lucy  has  arrived  at  the  following  re- 
sults : — 


Species. 

Weight  of  AnimaL  Surface  of  Wings. 

Surface  per 
Kilogramme. 

Gnat  . 
Butterfly. 
Pigeon 
Stork  . 
Australian  Crane. 

3  milligr. 
20  centigr. 
290  grammes. 
2265  „ 
9500  „ 

30  sq.  millim. 
1663  ,, 
750  sq.  centim. 
4506  „  „ 
8543  „  „ 

10  sq.  millim. 

84,.  »\ 
2586   sq.  centim. 
1988    „  „ 
899    „  „ 

From  these  measurements  we  obtain  the  following  im- 
portant consideration,  that  animals  of  large  size  and  great 
weight  sustain  themselves  in  the  air  with  a  much  less  pro- 
portionate surface  of  wing  than  those  of  smaller  size. 

Such  a  result  plainly  shows  that  the  part  played  by  the 
wing  in  flight  is  not  merely  passive,  for  a  sail  or  a  parachute 
ought  always  to  have  a  surface  in  proportion  to  the  weight 
which  it  has  to  support;  but,  on  the  contrary,  when  con- 
sidered in  its  proper  point  of  view,  as  an  organ  which  strikes 
the  air,  the  wing  of  the  bird  ought,  as  we  shall  see,  to  pre- 


FORM  OF  THE  BIRD. 


225 


sent  a  surface  relatively  less  in  birds  of  large  size  and  of 
great  weight. 

The  surprise  which  we  feel  at  the  result  obtained  by  Mons. 
de  Lucy  disappears  when  we  consider  that  there  is  a  geome- 
trical reason  why  the  surface  of  the  wing  cannot  increase  in 
the  ratio  of  the  weight  of  the  bird.  In  fact,  if  we  take  two 
objects  of  the  same  form — two  cubes,  for  example — one  of 
which  has  a  diameter  twice  as  large  as  the  other,  each  of  the 
surfaces  of  the  larger  cube  will  be  four  times  as  large  as  that 
of  the  smaller  one,  but  the  weight  of  the  large  cube  will  be 
eight  times  that  of  the  small  one. 

Thus,  for  all  similar  geometrical  solids,  the  linear  dimen- 
sions being  in  a  certain  ratio,  the  surfaces  will  increase  in 
proportion  to  their  squares,  and  the  weights  in  that  of  their 
cubes.  Two  birds  similar  in  form,  one  of  which  has  an 
extent  of  wing  twice  as  large  as  the  other,  will  have  wing 
surfaces  in  the  proportion  of  one  to  four,  and  weights  in  that 
of  one  to  eight. 

Dr.  Hureau  de  Villeneuve,  basing  his  enquiries  on  these 
considerations,  has  determined  the  surface  of  wing  which 
would  enable  a  bat  having  the  weight  of  a  man  to  fly ;  and 
he  has  found  that  each  of  the  wings  need  not  be  three  metres 
in  length. 

In  a  remarkable  work  on  the  relative  extent  of  wing  and 
weight  of  pectoral  muscles  in  different  species  of  flying  ver- 
tebrate animals,*  Hartings  shows  that  in  a  series  of  birds  we 
can  establish  a  certain  relation  between  the  surface  of  the 
wing  and  the  weight  of  the  body.  But  we  must  be  careful 
only  to  compare  elements  which  admit  of  comparison;  for 
instance,  the  length  of  the  wings,  the  square  roots  of  their 
surfaces,  and  the  cube  roots  of  the  weights  of  different  birds. 

Let  I  be  the  length  of  the  wing ;  a,  its  area  or  surface ; 
aiul  p  the  weight  of  the  body;  we  can  compare  together 
and  y/p. 

Making  observations  on  different  types  of  birds,  Hartings 
ascertained  their  measurements  and  weights,  from  which  he 
obtained  the  following  table  : — 


*  Archives  Neerlamlaises,  Vol.  XIV.,  p.  1869. 


224 


ANIMAL  MECHANISM. 


Name  of  Species. 

Weight. 
P 

Surface. 
a 

Ratio. 
VP 

1. 

Larus  argentatus    .  • 

ODO  U 

041 

2. 

Anas  nyroca      .       •       .  . 

ovo  u 

OA  1 

/  AO 

3. 

Fulica  atra  .... 

4t>0  U 

OAK 

z  uo 

4. 

Anas  crecca       .       •       •  . 

Z(  O  0 

1  A  A 

144 

1  *84 

5. 

Larns  ridihundus    •       •  * 

i  q7  .a 
lvt  0 

331 

3*13 

6. 

Machetes  pugnax      •       .  . 

1  QO  -O 

i  yu  o 

i  a  A 
1d4 

2 '23 

7. 

Rallus  aquaticus    .  • 

1  1  u  o 

IV  I 

1  .Ql 

1  ol 

8. 

Turdus  pilaris   .       .       .  . 

103  '4 

i  ni 

1U1 

A  J.4 

9. 

Turdus  merula       .  • 

88  8 

J.UO 

10. 

Sturnus  vulgaris       .       •  . 

86-4 

85 

2-09 

11. 

Bombicilla  garrula .  • 

60'0 

44 

1-69 

12. 

Alauda  arvensis.       •       •  . 

32-2 

75 

2.69 

13. 

Par  us  major  .... 

14-5 

31 

2-29 

14. 

Fringilla  spinus        .       .  . 

10-1 

25 

2-33 

15 

Parus  cceruleus 

91 

24 

2-34 

To  this  list  of  Hartings  we  will  add  another  which  we  have 
prepared  by  the  same  method  (p.  225).  All  the  experiments  have 
been  made  on  birds  killed  by  the  gun,  and  a  few  instants  after 
death.  We  have  taken  the  surface  of  the  two  wings  instead 
of  only  one,  as  Hartings  had  done ;  this  modification,  which 
appeared  necessary,  is  the  principal  cause  of  the  difference 
which  the  reader  will  find  between  our  numbers  and  those  of 
the  Dutch  physiologist.  To  compare  the  two  tables,  it  will 
be  necessary  to  multiply  by  \/2  the  number  obtained  by 

Hartings  as  the  expression  of  the  ratio  ^ 

The  variations  that  we  find  in  the  ratio  of  the  weight  of 
the  body  to  the  surface  of  the  wings  in  different  species  of 
birds,  depends  in  a  great  degree  on  the  form  of  the  wings. 
In  fact,  it  is  not  immaterial  whether  the  surface  which  strikes 
the  air  has  its  maximum  near  the  body  or  near  the  extremity ; 
these  two  points  have  very  different  velocities.  For  an  equal 
extent  of  surface  the  resistance  will  be  greater  at  the  point  of 
the  wing  than  at  its  base.  It  follows  from  this,  that  two  birds 
of  unequal  surface  of  wing  may  find  in  the  air  an  equal  resist- 
ance, provided  that  these  surfaces  are  differently  arranged. 

The  weight  of  the  pectoral  muscles  is,  on  the  contrary,  in 
a  simple  ratio  to  the  total  weight  of  the  bird,  and  notwith- 


FORM  OF  THE  BIRD. 


2^5 


standing  variations  which  correspond  with  the  different  apti- 
tudes for  flight  with  which  each  species  is  endowed,  we  find 
that  it  is  about  one- sixth  of  the  whole  weight  in  the  greater 
number  of  birds. 


Name  of  Species. 

Weight  =  p. 
Grammes. 

Surface  of 
Wings  =  2a. 
Square  centi 
metres. 

Ratio  =  Y^Z 
VP 

vuitur     .      .  • 

*l  RR'i  -OA 

616  L 

4*722 

Vultur  cinereus    .       •  . 

1000  UU 

oooo 
6166 

a  •non 

4  yzy 

X'  dXUU  l/lilliUliUUlUo         •  • 

128 '94 

RAO 

O  UJD 

tt          , ,       minor .  • 

Itl  oo 

040 

A -AO  A 
4  4Z4 

raico  ivoDeic     .  . 

OQO  -A  A 

ZoZ  44 

y/u 

A  '*7  A  *r 
4/4/ 

Jc  aico  8UDiatlO  (r^   .  . 

ouy  oz 

10o4 

0  loo 

Falco  palustris  .  • 

ZUO  /O 

1188 

5  '81 0 

Falco  milvus       •      .  . 

OZU  14 

1  (1(\A 

iyu4 

0  11/ 

Strix  passerina  .  • 

izz  ov 

394 

3*993 

»>_       »>           •       •  • 

*l  9S'Q4 

i  zo  y4 

A  AO 

44Z 

>4  •!  «0 

4  lOZ 

Saxicola  oeiianthe  • 

KR  -f\K 

00  uo 

1  OK 

lzo 

o  .noo 

z  yzz 

Alauda  cristata     .       •  . 

%r  sin 

ono 

4  Z/O 

Corvus  comix    .  . 

Q7  A  .KA 

61 4  04 

1 1  oo 

4  /I  t 

Upupa  epops       .       .  . 

4y  iz 

329 

4*952 

Merops  apiaster.  . 

10  60 

117 

4*105 

Alcedo  ispida       .       .  . 

82-89 

270 

3  769 

Alcedo  afra  (?)  . 

85*96 

288 

3*845 

Columba  vinacea  .       .  . 

11200 

292 

3  545 

Vanellus  spihosus 

159  64 

636 

4*649 

Glareola       .       .       .  . 

95-17 

343 

4*056 

Buteo  vulgaris  .  . 

785-00 

1651 

4*405 

Perdix  cinerea      .       .  . 

280-00 

320 

2*734 

Sturnus  vulgaris  . 

78-00 

202 

3  326 

Corvus  pica  .       .      •  . 

21200 

540 

3  906 

>>      »»         •       •  • 
Hirundo  urbica    .       .  . 

275  00 

690 

4  039 

18-00 

120 

4-180 

Turdus  merula  . 

94  00 

230 

3  335 

In  conclusion,  each  animal  which  sustains  itself  in  the  air 
must  develop  work  proportionate  to  its  weight ;  it  ought,  for 
this  purpose,  to  possess  muscular  mass  in  proportion  to  this 
weight ;  for,  as  we  have  already  seen,  if  the  actions  performed 
by  the  muscles  of  birds  are  always  of  the  same  nature,  these 
actions  and  the  work  which  they  perform  will  be  in  proportion 
to  the  mass  of  the  muscles. 


226 


ANIMAL  MECHANISM. 


But  how  is  it  that  wings  whose  surfaces  vary  as  to  the 
square  of  their  linear  dimensions  are  sufficient  to  move  the 
weights  of  birds  which  vary  in  the  ratio  of  the  cubes  of  these 
dimensions  ? 

It  can  be  proved  that,  if  the  strokes  of  the  wing  were  as 
frequent  in  large  as  in  small  birds,  each  stroke  would  have  a 
velocity  whose  value  would  increase  with  the  size  of  the  bird ; 
and  as  the  resistance  of  the  air  increases  for  each  element  of 
the  surface  of  the  wing,  according  to  the  square  of  the  velo- 
city of  that  organ,  a  considerable  advantage  would  result  to 
the  bird  of  large  size,  as  to  the  work  produced  upon  the  air. 

Hence  it  follows,  that  it  would  not  be  necessary  for  large 
birds  to  give  such  frequent  strokes  of  the  wing  in  order  to 
sustain  themselves  as  would  be  required  for  those  of  smaller 
size. 

Observers  have  not,  hitherto,  been  able  to  determine  very 
accurately  the  number  of  the  strokes  of  the  wing,  in  order  to 
ascertain  whether  their  frequency  is  in  an  exact  inverse  ratio 
to  the  size  of  birds ;  but  it  is  easy  to  see  that  the  number  of 
strokes  varies  in  birds  of  different  size  in  a  proportion  of  this 
kind. 


CHAPTER  IV. 

OF  THE  MOVEMENTS  OF  THE  WING  OF  THE  BIRD 
DURING  FLIGHT. 

Frequency  of  the  movements  of  the  wing — Relative  durations  of  its  rise 
and  fall— Electrical  determination — Myographical  determination. 

Trajectory  of  the  bird's  wing  during  flight— Construction  of  the  instru- 
ments which  register  this  movement — Experiment — Elliptical  figure 
of  the  trajectory  of  the  point  of  the  wing. 

In  the  general  remarks  on  the  form  of  the  bird,  and  on  the 
deductions  to  be  drawn  from  it,  the  reader  must  have  seen 
that  many  hypotheses  await  experimental  demonstration.  For 
this  reason,  we  have  been  anxious  to  apply  to  the  flights  of 


MOVEMENTS  OF  THE  WINGS  OF  BIRDS. 


227 


the  bird  the  method  which  has  enabled  us  to  analyse  the  other 
modes  of  locomotion. 

Frequency  of  the  strokes  of  the  wing. — The  graphic  method 
which  enabled  us  so  easily  to  determine  the  frequency  of  the 
strokes  of  the  insect's  wing  cannot  be  employed  under  the  same 
conditions  when  we  experiment  on  the  bird.  It  will  be  neces- 
sary to  transmit  signals  between  the  bird  as  it  flies  and  the 
registering  apparatus.  We  have  here  to  deal  with  a  problem 
similar  to  that  which  we  solved  with  respect  to  terrestrial 
locomotion,  when  we  registered  the  number  and  the  relative 
duration  of  the  pressures  of  the  feet  upon  the  ground.  We 
must  now  estimate  the  duration  of  the  impacts  of  the  wing 
upon  the  air,  and  the  time  which  it  occupies  in  its  rising 
motion. 

Electrical  method. — We  made  use  at  first  of  the  electric 
telegraph.  The  experiments  consist  in  placing  on  the  ex- 
tremity of  the  wing  a  kind  of  apparatus  which  breaks  or  closes 
an  electric  circuit  at  each  of  the  alternate  movements  which 
it  is  induced  to  make.  In  this  circuit  is  placed  an  electro- 
magnetic arrangement  which  writes  upon  a  revolving  cylinder. 
Figure  94  shows  this  mode  of  telegraphy  applied  to  the  study 
of  a  pigeon's  flight,  simultaneously  with  the  transmission  of 
signals  of  another  kind,  to  be  hereafter  described.  In  this 
figure  the  two  conducting  wires  are  separated  from  each  other. 

The  writing  point  will  trace  a  wavy  line,  the  elevations  and 
depressions  of  which  will  correspond  with  each  change  in  the 
direction  of  the  movement  of  the  wing.  In  order  that  the 
bird  may  fly  as  freely  as  possible,  a  thin  flexible  cable,  con- 
taining two  conducting  wires,  establishes  a  communication 
between  the  bird  and  the  telegraphic  tracing  point.  The  two 
ends  of  the  wires  are  fastened  to  a  very  small  light  instrument 
which  acts  like  a  valve  under  the  influence  of  the  resistance  of 
the  air.  When  the  wing  rises,  the  valve  opens,  the  current 
is  broken,  and  the  line  of  the  telegraphic  tracing  rises.  When 
the  wing  descends,  the  valve  closes,  the  current  closes  at  the 
same  time,  and  the  tracing  made  by  the  telegraph  is  lowered. 

This  instrument,  when  applied  to  different  kinds  of  birds, 
enables  us  to  ascertain  the  frequency  peculiar  to  the  move- 
ments of  each.    The  number  of  species  which  we  have  been 


228 


ANIMAL  MECHANISM. 


able  to  study  is  very  small  as  yet ;  the  following  are  the 
results  obtained : — 

Revolutions  of  wing 
per  second. 


Sparrow .......  13 

Wild  duck   9 

Pigeon   8 

Moor  buzzard    5| 

Screech  owl   5 


Buzzard   3 

The  frequency  of  the  strokes  of  the  wing  varies  also,  according 
as  the  bird  is  first  starting,  in  full  flight,  or  at  the  end  of  its 
flight.  Some  birds,  as  we  know,  keep  their  wings  perfectly 
still  for  a  time ;  they  glide  upon  the  air,  making  use  of  the 
velocity  already  acquired. 

Relative  duration  of  the  depression  and  elevation  of  the  wing  — 
Contrary  to  the  opinion  entertained  by  some  writers,  the 
duration  of  the  depression  of  the  wing  is  usually  longer  than 
that  of  its  rise.  The  inequality  of  these  two  periods  is  more 
distinctly  seen  in  birds  whose  wings  have  a  large  surface,  and 
which  beat  slowly.  Thus,  while  the  durations  are  almost 
equal  in  the  duck,  whose  wings  are  very  narrow,  they  are 
unequal  in  the  pigeon,  and  still  more  so  in  the  buzzard. 
The  following  are  the  results  of  our  experiments : — 


Total  duration  of  a 
revolution  of  the  wing. 

Ascent. 

Descent. 

Duck 

Pigeon        .  . 
Buzzard  . 

11|  hundreds  of  a  second  . 
324 

5 
4 

61 
84 
20 

It  is  more  difficult  than  would  have  been  expected,  to  determine 
the  precise  instant  when  the  direction  of  the  line  traced  by  the 
telegraph  changes.  The  periods  during  which  the  soft  iron 
is  first  attracted  and  then  set  free,  have  an  appreciable  duration 
when  the  blackened  cylinder  turns  with  sufficient  rapidity  to 
enable  us  to  measure  the  rapid  movements  which  are  the 
subjects  of  this  inquiry.  The  inflections  of  the  line  traced  by 
the  telegraph  then  become  curves,  the  precise  commencement 


MOVEMENTS  OF  THE  WINGS  OF  BIKDS.  229 


of  each  of  which  it  is  difficult  to  discover.  There  is  therefore 
some  limit  to  the  precision  of  the  measurements  which  we  can 
take  by  the  electric  method ;  we  can  still,  however,  estimate 
by  this  means  the  duration  of  a  movement  with  a  tolerably 
accurate  approximation. 

Myographic  method. — We  have  seen  that  a  dilatation  accom- 
panies the  contraction  of  the  muscles,  and  follows  it  through 
all  its  phases.  A  shortening  of  the  muscle,  either  rapid  or 
slow,  feeble  or  energetic,  as  the  case  may  be,  will  therefore  be 
accompanied  by  a  lateral  dilatation  which  will  have  similar 
characters  of  rapidity  or  intensity.  At  each  depression  of  the 
wing  of  a  bird,  the  large  pectoral  muscles  will  be  subject  to  a 
dilatation  which  it  will  be  necessary  to  transmit  to  the  re- 
gistering apparatus. 

We  shall  have  recourse,  for  this  purpose,  to  the  apparatus 
which  we  have  employed  in  determinations  of  the  same  kind, 
when  treating  of  human  locomotion.  Some  slight  modifica- 
tions will  enable  them  to  give  signals  of  the  alternate  phases 
of  dilatation  and  relaxation  of  the  large  pectoral  muscle. 


Fig  93.— Apparatus  to  investigate  the  contraction  of  the  thoracic  muscles 
of  the  bird.  The  upper  convex  surface  is  formed  or  a  membrane  of  india- 
rubber  supported  by  a  spiral  spring ;  this  part  is  applied  to  the  muscles. 
The  lower  surface,  in  contact  with  the  corset,  carries  four  small  hooks 
which  are  fastened  in  the  stuff  and  keep  the  instrument  in  its  place. 


The  bird  flies  in  a  space  fifteen  metres  square  and  eight 
metres  high.  The  registering  apparatus  being  placed  in  the 
centre  of  the  room  where  the  experiment  is  made,  twelve 
metres  of  india-rubber  tubing  are  sufficient  to  establish  a 
constant  communication  between  the  bird  and  the  apparatus. 

A  sort  of  corset  is  fixed  on  a  pigeon  (see  figure  94).  Under 
this  corset,  between  the  stuff,  which  is  tightly  stretched,  and 


230 


ANIMAL  MECHANISM. 


the  pectoral  muscles,  a  small  instrument  is  slipped,  which  is 
intended  to  show  the  dilatation  of  the  muscles,  and  is  constructed 
in  the  following  manner : 

A  little  metal  pan  (fig.  93),  containing  within  it  a  spiral 
spring,  is  closed  by  a  membrane  of  india-rubber.  This  closed 
pan  communicates  with  a  tube  transmitting  air. 


Fig.  94.— Experiment  to  determine  by  the  electrical  and  myograpbical 
methods,  at  the  same  time,  the  frequency  of  the  movements  of  the  wing 
and  the  relative  durations  of  its  elevation  and  depression. 


Each  pressure  on  the  india-rubber  membrane  depresses 
it,  and  the  spring  gives  way ;  the  air  is  driven  out  of  the  pan, 
and  escapes  by  the  tube.  When  the  pressure  ceases,  the  air 
is  returned  to  the  instrument  by  the  elasticity  of  the  spring 


MOVEMENTS  OF  THE  WINGS  OF  BIRDS.  231 


which  raises  the  membrane.  Alternate  outward  and  inward 
currents  of  air  are  thus  established  in  the  tube,  and  this 
movement  transmits  to  the  registering  apparatus  the  signals 
of  the  less  or  greater  pressures  exerted  on  the  membrane  of 
the  small  pan. 

The  registering  instrument  is  the  lever  drum,  with  which 
the  reader  is  already  acquainted.  It  gives  an  ascending  curve 
while  the  muscle  contracts,  and  a  descending  one  when  it  is 
relaxed. 

Fig.  94  represents  the  general  arrangement  of  the  experi- 
ment, in  which  the  electric  telegraph  and  the  transmission  of 
air  are  used  at  the  same  time. 

It  shows  a  pigeon  fitted  with  a  corset,  under  which  is 
slipped  the  instrument  which  is  to  show  the  action  of  the 
pectoral  muscles.  The  transmitting  tube  ends  in  a  registering 
apparatus,  which  writes  on  a  revolving  cylinder. 

At  the  extremity  of  the  pigeon's  wing  is  the  instrument 
which  opens  or  closes  an  electric  current,  as  the  wing  rises 
or  sinks.  The  two  wires  of  the  circuit  are  represented  as 
separated  from  one  another ;  within  the  circuit  are  seen  two 
elements  of  Bunsen's  pile,  and  the  electro-magnet  which, 
being  furnished  with  a  lever,  registers  the  telegraphic  signals 
of  the  movements  of  the  wing. 

Experiment. — The  bird  is  set  free  at  one  extremity  of  the 
room,  the  dove-cot  in  which  it  is  usually  kept  being  placed 
at  the  opposite  end.  The  bird  as  it  flies  naturally  seeks  its 
nest  in  which  to  rest.  During  its  flight  we  obtain  the  tracings 
represented  by  fig.  95. 

It  is  seen  that  the  tracings  differ  according  to  the  kind  of 
bird  on  which  the  experiment  is  made.  However,  we  ob- 
serve in  each  of  the  tracings  the  periodical  return  of  the  two 
movements  a  and  b,  which  are  produced  at  each  revolution  of 
the  wing. 

On  what  do  these  two  muscular  acts  depend  ?  It  is  easy 
to  discover  that  the  undulation  a  corresponds  with  the  muscle 
that  elevates  the  w  ing,  and  6  with  that  which  depresses  it. 
This  can  be  proved  :  first,  by  collecting,  at  the  same  time  as 
the  muscular  tracing,  those  of  the  ascending  and  descending 
movements  of  the  wing  transmitted  by  electricity.  When 


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MOVEMENTS  OF  THE  WINGS  OF  BIRDS.  233 


these  two  tracings  are  placed  over  each  other,  they  show  that 
the  time  of  the  elevation  of  the  wing  agrees  with  the  dura- 
tion of  the  undulation  a,  and  the  time  of  its  depression  coin- 
cides with  the  undulation  b. 

From  this  we  may  see  how  the  undulations  a  and  b  are 
produced  in  all  the  muscular  tracings  obtained  from  birds. 
In  fact,  close  by  the  portion  of  the  bird's  breast  on  which  the 
experiment  is  made,  and  near  the  projecting  edge  of  the 
sternum,  there  are  two  distinct  layers  of  muscle ;  the  more 
superficial  one  is  formed  by  the  large  pectoral,  the  depressor 
of  the  wing ;  the  deeper  one  by  the  middle  pectoral,  or  ele- 
vator of  the  wing,  whose  tendon  passes  behind  the  forked 
part  of  the  sternum  to  attach  itself  to  the  head  of  the 
humerus. 

These  two  muscles,  being  superposed,  will  act  by  their 
dilatation  on  the  apparatus  applied  to  them  ;  the  elevator  of 
the  wing,  swelling  as  it  contracts,  gives  its  signal  by  the  un- 
dulation a ;  the  great  pectoral  signals  the  depression  of  the 
wing  by  the  undulation  b. 

We  may  verify  the  correctness  of  this  explanation  by  means 
of  a  very  simple  experiment.  Anatomy  shows  us  that  the 
muscle  which  elevates  the  wing  is  narrow,  and  only  covers  the 
depressor  in  its  most  inward  part,  situated  along  the  ridge 
of  the  sternum  ;  so  that  if  we  displace  the  little  apparatus 
which  shows  the  movement  of  the  muscles,  and  remove  it  a 
little  outwards,  it  will  occupy  a  part  where  the  depressor  of 
the  wing  is  not  covered  by  the  elevator,  and  the  tracing 
will  only  present  a  simple  undulation,  corresponding  with 
b  in  the  curves  of  fig.  95.  It  is  thus  plainly  shown  tnat  the 
undulations  a  and  b  in  the  muscular  tracings  of  the  birds  on 
which  we  have  experimented  correspond  exactly  with  the 
actions  of  the  principal  muscles  which  elevate  and  depress 
the  wing ;  but  we  cannot  attach  great  importance  to  the  form 
of  the  tracings,  in  order  to  deduce  from  them  the  precise 
nature  of  the  movement  performed  by  the  muscle.  These 
movements  seem,  in  fact,  to  encroach  on  each  other ;  so  that 
the  relaxation  of  the  elevator  of  the  wing  is  probably  not 
completed  when  the  depressor  begins  to  act. 

We  expect  nothing  more  from  these  tracings  than  that 
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234 


ANIMAL  MECHANISM. 


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which  they  more  readily  furnisli ; 
namely,  the  number  of  the  revolu- 
tions of  the  wing,  the  greater  or  less 
regularity  of  these  movements,  and 
the  equality  or  inequality  of  each  of 
them. 

Confining  the  question  within 
these  limits,  experiment  shows  that 
the  strokes  of  the  bird's  wing  differ 
in  amplitude  and  in  frequency  from 
one  moment  to  another  as  they  fly. 
When  they  first  start,  the  strokes 
are  rather  fewer,  but  much  more 
energetic  ;  they  reach,  after  two  or 
three  strokes  of  the  wing,  a  rhythm 
almost  regular,  which  they  lose 
again  when  they  are  about  to  settle 
(fig.  96). 

TRAJECTORY  OF  THE  WING  OF  THE 
.BIRD   DURING  FLIGHT. 

We  have  seen,  when  treating  of 
the  mechanism  of  insect  flight,  that 
the  fundamental  experiment  was 
that  which  revealed  to  us  the  course 
of  the  point  of  the  wing  throughout 
each  of  its  revolutions.  Our  know- 
ledge of  the  mechanism  of  flight 
naturally  flowed,  if  we  may  so  say, 
from  this  first  notion. 

The  same  determination  is  equally 
necessary  for  the  flight  of  birds ; 
but  the  optical  method  is  unsuitable 
for  this  purpose.  In  fact,  the  move- 
ment of  the  bird's  wing,  although 
too  rapid  to  be  appreciable  by  the 
eye,  is  not  sufficiently  so  to  furnish 
such  a  persistent  impression  on  the 
retina  as  to  show  its  whole  course. 


MOVEMENTS  OF  THE  WINGS  OF  BIKDS.  235 


The  graphic  method,  with  its  transmission  of  signals,  which 
we  have  hitherto  employed,  only  furnishes  the  expression  of 
movements  which  take  place  in  a  straight  line,  such  as  the 
contraction  or  lengthening  of  a  muscle,  the  vertical  and  hori- 
zontal oscillations  of  the  body  during  the  act  of  walking,  &c. 
It  is  only  by  combining  this  rectilinear  movement  with  the 
uniform  advance  of  the  smoked  surface  that  receives  the 
tracing,  that  we  obtain  the  expression  of  the  velocity  with 
which  the  movement  at  each  instant  is  effected. 

The  action  of  the  wing  during  flight  does  not  consist 
merely  of  alternate  elevations  and  depressions.  We  have  only 
to  look  at  a  bird  as  it  flies  over  our  head  to  ascertain  that  the 
wing  is  carried  also  forward  and  backward  at  each  stroke. 
From  this  double  action  must  result  a  curve  which  it  is  neces- 
sary to  describe. 

It  can  be  geometrically  shown  that  every  plane  figure, 
that  is  to  say,  every  figure  susceptible  of  being  described  upon 
a  plane  surface,  can  be  produced  by  the  rectangular  combina- 
tion of  two  rectilinear  movements.  The  tracings  obtained  by 
Koenig  by  arming  with  a  style  Wheatstone's  vibrating  rods, 
and  the  luminous  figures  of  musical  chords  which  Lissajous 
produced  by  the  reflection  of  a  pencil  of  light  upon  two 
mirrors  vibrating  perpendicularly  to  each  other,  are  well- 
known  examples  of  the  formation  of  a  plane  figure  by  means 
of  two  rectilinear  movements  at  right  angles  to  each  other. 

Thus,  if  we  can  transmit  at  the  same  time  the  movements 
of  elevation  and  depression  executed  by  the  wing  of  the  bird, 
as  well  as  those  which  the  organ  makes  forwards  and  back- 
wards ;  then,  supposing  that  a  tracing  point  can  receive  simul- 
taneously the  impulse  of  these  two  movements  at  right  angles 
to  each  other,  this  point  will  describe  on  the  paper  the  exact 
tracing  of  the  movements  of  the  bird's  wing. 

We  have  endeavoured  first  to  construct  an  instrument  which 
would  thus  transmit  to  a  distance  any  movement  whatever, 
and  register  it  on  a  plane  surface,  without  attending  to  the 
method  by  which  this  machine,  which  may  be  more  or  less 
heavy,  might  be  adapted  to  the  body  of  the  bird.  Fig.  97 
represents  our  first  experimental  instrument,  the  description 
of  which  is  indispensable  in  order  to  enable  our  readers  to 


236 


ANIMAL  MECHANISM. 


understand  the  construction  of  the  machine  which  we  finally 
employed. 

Od  two  solid  feet  carrying  vertical  supports,  we  placed 
two  horizontal  arms  parallel  to  each  other.  These  were  two 
aluminium  levers,  which,  by  means  of  the  apparatus  we  are 
about  to  describe,  will  both  execute  the  same  movements. 
Each  of  these  levers  is  mounted  on  a  Cardan  joint,  that  is  to 
say,  a  universal  joint  which  allows  every  kind  of  movement ; 
so  that  each  lever  can  be  carried  upwards,  downwards,  to 
the  right  or  the  left ;  it  can  describe  with  its  point  the  base 
of  a  cone  of  which  the  Cardan  forms  the  apex  ;  in  fact  it  will 
execute  any  kind  of  movement  which  the  experimenter  may 
please  to  give  it. 

It  was  requisite  to  effect  the  transmission  of  the  move- 
ments of  one  of  these  levers  to  the  other,  and  that  at  a  dis- 
tance often  or  fifteen  metres.  This  is  done  by  a  method  with 
which  the  reader  is  already  acquainted — the  employment  of 
air-drums  and  tubes. 

The  lever,  which  in  fig.  97  is  seen  to  the  left  hand,  is 
fastened  by  a  vertical  metallic  wire  to  the  membrane  of  a 
drum  placed  underneath  it.  In  the  vertical  movements  of 
the  lever,  the  membrane  of  the  drum,  alternately  depressed 
and  raised,  will  produce  a  current  of  air,  which  will  be  trans- 
mitted by  a  long  air-tube  to  the  membrane  of  a  similar  drum 
belonging  to  the  apparatus  on  the  right  hand.  The  second 
drum,  placed  above  the  lever  which  corresponds  with  it,  and 
is  fastened  to  it,  will  faithfully  transmit  all  the  vertical 
movements  which  have  been  given  to  drum  No.  1  (that  on 
the  left).  The  motion  of  the  two  levers  will  be  in  the  same 
direction,  on  account  of  the  inversion  of  the  position  of  the 
drums. 

Let  us  suppose  that  we  lower  the  lever  No.  1  ;  we  com- 
press the  membrane  of  the  drum  beneath  it;  a  current  of 
air  is  produced  which  raises  the  membrane  of  the  second 
drum,  and  consequently  lowers  lever  No.  2.  On  the  contrary, 
the  elevation  of  lever  No.  1  will  produce  an  inward  current  of 
air,  which  will  raise  the  membrane  and  the  lever  of  No.  2. 

Proceeding  in  the  same  manner  for  the  transmission  of 
movements  in  the  horizontal  plane,  we  place  to  the  right  of 


238 


ANIMAL  MECHANISM. 


one  of  the  levers  and  to  the  left  of  the  others,  a  drum  whose 
membrane,  situated  in  the  vertical  plane,  acts  in  a  lateral 
direction;  the  transmission  of  these  movements  is  made  by  a 
special  tube,  as  in  the  case  of  the  vertical  movements. 

The  apparatus  having  been  thus  constructed,  if  we  take  in 
our  fingers  the  extremity  of  one  of  the  levers,  and  give  it  any 
motion  whatever,  we  shall  see  the  other  lever  repeat  it  with 
perfect  fidelity. 

All  the  difference  consists  in  a  slight  diminution  of  the  am- 
plitude of  the  movements  in  the  second  lever.  This  is  because 
the  air  contained  in  each  of  the  systems  of  tubes  and  drums 
is  slightly  compressed,  and  consequently  does  not  transmit 
completely  the  movement  which  it  receives.  It  would  be  easy 
to  remedy  this  inconvenience,  if  it  were  found  to  be  one,  by 
giving  to  the  receiving  apparatus  a  greater  sensibility,  which 
might  be  effected  by  placing  the  Cardan  joint  a  little  nearer 
the  point  where  the  movement  is  transmitted  to  the  lever  of 
the  second  instrument.  But  it  is  better  not  to  seek  to  amplify 
the  movements  too  much  when  we  wish  to  register  them  by 
tracings,  since  we  then  augment  the  friction,  and  diminish  the 
force  by  which  it  must  be  overcome. 

After  having  ascertained  that  the  transmission  of  any  move- 
ment whatever  is  effected  in  a  satisfactory  manner  by  this  ap- 
paratus, we  sought  for  a  means  of  tracing  this  movement  on  a 
plane  surface.  The  difficulty  which  occurred  in  the  application 
of  the  graphic  method  to  the  study  of  the  movement  of  the 
insect's  wing,  again  presents  itself  here  ;  but  in  this  case  there 
are  no  means  of  avoiding  it  by  taking  only  partial  tracings. 

The  point  of  the  lever  No.  2  describes  in  space  a  spherical 
figure  incapable  of  becoming  tangential,  except  in  a  single 
point,  to  the  smoked  surface  which  is  to  receive  the  tracing. 
Consequently,  it  has  been  necessary  to  register  the  projection 
of  this  figure  on  a  plane  surface,  and  to  arrange  the  lever  in 
such  a  manner  that  it  may  lengthen  or  shorten  itself  as  re- 
quired, in  order  to  keep  always  in  contact  with  the  smoked 
glass.  This  result  was  obtained  by  means  of  a  spring  which 
served  as  a  writing  point. 

Fig.  98  shows  the  spring  in  question,  at  the  extremity  of  a 
lever.    It  is  wide  at  the  base,  in  order  to  resist  any  tendency 


MOVEMENTS  OF  THE  WINGS  OF  BIRDS.  239 


to  lateral  deviations  under  the  influence  of  the  friction ;  this 
base  is  fixed  to  a  vertical  piece  of  aluminium,  which  is 
attached  by  its  lower  part  to  the  extremity  of  the  lever.  In 
this  manner,  the  point  of  the  spring  which  acts  as  a  style  is 
considerably  in  front  of  the  lever  whose  movements  it  is  to 
register.  Let  us  suppose  the  lever  to  rise,  and  take  the 
position  indicated  by  the  dotted  line  in  figure  98  ;  while 
traversing  this  space,  it  will  have  described  an  arc  of  a  circle, 
and  its  extremity  will  no  longer  be  in  the  same  plane  as  before, 
but  the  elasticity  of  the  spring  will  have  carried  the  writing 
point  more  forward ;  it  will  still  continue,  therefore,  to  be 


Fig.  98.— Elastic  point  tracing  on  a  smoked  glass. 


in  contact  with  the  plane  on  which  it  is  to  trace.  Thus  the 
lever  lengthens  or  shortens,  as  required,  and  its  point 
always  presses  on  the  plane.  The  surface  on  which  the  tracing 
is  received  is  a  well-polished  glass,  and  the  spring  which 
forms  the  style  is  so  flexible,  that  the  elastic  pressure  which  it 
exerts  upon  the  glass  rubs  it  but  slightly. 

The  apparatus  being  thus  arranged,  it  must  be  submitted 
to  a  verifying  process,  to  ascertain  if  movements  are  faithfully 
transmitted  and  registered. 

For  this  purpose,  arming  the  two  levers  of  fig.  97  with 
similar  styles,  we  placed  their  points  against  the  same  piece 
of  smoked  glass ;  we  directed  with  the  hand  one  of  the  levers 
so  as  to  trace  any  figure,  to  sign  one's  name  for  instance ;  the 
other  lever  ought  to  trace  the  same  figure,  to  reproduce  the 
same  signature. 


240 


ANIMAL  MECHANISM. 


It  generally  happens  that  the  transmission  is  not  equally 
easy  in  both  directions  ;  we  perceive  a  slight  deformity  in  the 
transmitted  figure,  which  is  lengthened  more  or  less  both  in 
height  and  in  width.  This  fault  can  always  be  corrected  ;  it 
arises  from  the  fact,  that  the  membrane  of  one  of  the  drums, 
being  more  stretched  than  that  of  the  other,  obeys  less  easily. 
We  soon  succeed,  by  various  trials,  in  giving  the  same  sensi- 
bility to  the  two  membranes,  which  is  ascertained,  when  we 
find  that  the  figure  traced  by  the  first  lever  is  identical  with 
that  of  the  second. 

Experiment  to  determine  graphically  the  trajectory  of  the  wing. 
— The  following  are  the  modifications  which  allow  us  to  apply 
this  mode  of  transmission  to  the  study  of  the  movements  of 
the  wing  of  a  flying  bird. 

As  the  apparatus  must  necessarily  be  of  considerable  weight, 
we  chose  a  large  bird  to  carry  it ;  strong  full-grown  buzzards 
were  employed  in  these  experiments.  By  means  of  a  kind  of 
corset  which  left  both  the  wings  and  the  legs  at  liberty,  we  fixed 
on  the  back  of  the  bird  a  thin  piece  of  light  wood  on  which 
the  apparatus  was  placed. 

In  order  that  the  lever  might  execute  faithfully  the  same 
movements  as  the  wing,  it  was  necessary  to  place  the  Cardan 
joint  of  this  lever  in  contact  with  the  humeral  articulation  of 
the  buzzard.  Therefore,  as  the  presence  of  the  drums  by  the 
side  of  the  lever  did  not  permit  this  immediate  contact,  we 
had  recourse  to  a  parallelogram,  which  transmitted  to  the  lever 
of  the  apparatus  the  movements  of  a  long  rod,  the  centre  of 
motion  in  which  was  very  near  the  articulation  of  the  bird's 
wing.  Then,  in  order  to  obtain  perfect  correspondence  be- 
tween the  movements  of  the  rod  and  those  of  the  buzzard's 
wing,  we  fixed  on  the  outer  edge  of  the  wing — that  is  to  say, 
on  the  metacarpal  bone  of  the  thumb  of  the  bird,  a  very  tight 
screw  clip,  furnished  with  a  ring,  through  which  slipped  the 
steel  rod,  of  which  we  have  before  spoken. 

Fig.  99  represents  the  buzzard  flying  with  the  apparatus 
just  described ;  underneath  it  hang  the  two  transmitting  tubes 
which  are  fixed  to  the  registering  instrument. 

After  a  great  many  fruitless  attempts  and  changes  in  the 
construction  of  the  apparatus,  which,  being  too  fragile,  broke 


242 


ANIMAL  MECHANISM. 


at  almost  every  flight  of  the  bird,  we  succeeded  in  obtaining 
satisfactory  results.    During  the  whole  of  the  bird's  flight  the 

registering  lever  described  a  kind 
of  ellipse.  This  ellipse,  registered 
on  a  plate  having  an  advancing 
movement  from  right  to  left,  gave 
figure  100.  In  order  to  under- 
stand this  figure,  we  must  imagine 
the  bird  flying  from  left  to  right 
(as  the  tracing  is  to  be  read), 
and  rubbing  the  extremity  of  its 
left  wing  against  a  wall  blackened 
with  smoke;  the  tracing  which 
its  wing  would  leave  under  these 
conditions  would  be  identical  with 
that  represented  in  fig.  100. 
This  curve  is  a  kind  of  ellipse 
spread  out  by  the  advancing  mo- 
tion of  the  plate  which  receives 
the  tracing.  Except  some  trem- 
blings of  the  line,  which  arose 
from  the  imperfection  of  the 
apparatus,  the  trajectory  of  the 
bird's  wing  may  be  compared  to 
the  tracing  given  under  the  same 
conditions  by  a  Wheatstone's  rod, 
tuned  in  unison,  and  giving  an 
elliptical  vibration. 

Fig.  101  represents  a  tracing 
of  this  kind. 

The  determination  of  the  course 
of  the  wing,  with  the  different 
phases  of  its  velocity,  is  so  im- 
portant, that  we  resolved  to  verify 
by  various  methods  the  reality 
of  this  elliptical  form.  All  our  ex- 
periments have  furnished  results 
w  hich  agree  with  each  other;  they  have  shown  that  birds  of  dif- 
ferent species  describe  with  their  wings  an  elliptical  trajectory. 


MOVEMENTS  OF  THE  WINGS  OF  BIRDS.  243 


D'Esterno  had  already  determined  by  his  experiments  that 
this  trajectory  existed ;  and  he  has  even  figured,  in  his  work, 
the  curve  described  ;  but,  in  his  opinion,  the  larger  axis  of 
the  ellipse  would  be  directed  downwards  and  backwards,  which 
is  entirely  opposed  to  the  result  of  our  experiments. 


Fig.  101. — Ellipse  formed  by  a  Wheatstone's  rod  tuned  in  unison,  and 
tracing  on  a  revolving  cylinder. 


We  remark  also  the  unequal  amplitude  of  the  strokes  of 
the  wing  from  the  commencement  to  the  end  of  fig.  100. 
This  variation  in  size  agrees  with  what  we  have  already 
stated  concerning  fig.  96.  This  showed  that  at  the  com- 
mencement of  its  flight,  the  bird  gives  stronger  strokes  with 
its  wing.  It  is  at  that  moment,  in  fact,  that  it  has  to  effect 
the  maximum  of  work,  in  order  to  rise  from  the  ground. 
After  this,  it  will  only  need  to  remain  at  the  height  which  it 
has  attained. 


ANIMAL  MECHANISM. 


CHAPTER  V. 

OF  THE  CHANGES  IN  THE  PLANE  OF  THE  BIRD'S  WING  AT 
DIFFERENT  POINTS  IN  ITS  COURSE. 

New  determination  of  the  trajectory  of  the  wing — Description  of  apparatus 
— Transmission  of  a  movement  by  the  traction  of  a  thread  Instru- 
ment and  apparatus  to  suspend  the  bird — Experiment  on  the  flight  of 
a  pigeon— Analysis  of  the  curves— Description  of  the  apparatus 
intended  to  give  indications  of  the  changes  in  the  plane  of  the  wing 
during  flight — Relation  of  these  changes  of  plane  with  the  other 
movements  of  the  wing. 

NEW  DETERMINATION   OF  THE   TRAJECTORY   OF   THE  WING. 

The  simultaneous  analysis  of  the  changes  in  the  plane  of 
the  wing,  and  of  the  various  phases  of  its  course,  would  have 
presented  great  difficulties,  if  we  had  not  discovered  a  new 
arrangement  of  the  apparatus,  which  allowed  us  to  examine, 
at  the  same  time,  an  almost  infinite  number  of  different 
movements. 

This  simplification  of  the  method  consists  in  the  employ- 
ment of  threads  to  transmit  the  movement  of  any  point 
whatever  to  the  experimental  apparatus,  which  in  its  turn, 
sends  it  by  the  ordinary  means  to  the  registering  instrument. 

Description  of  apparatus. — Let  fig.  102  be  two  lever-drums 
connected  together,  similar  to  those  already  represented  in 
fig.  21. 

The  lever  L  belongs  to  the  experimental  apparatus,  that  on 
which  the  movement  to  be  studied  is  to  act.  On  the  frame 
of  this  first  instrument  let  us  place  an  arm  of  bent  wire,  from 
the  extremity  of  which  an  india-rubber  thread,  F,  will  pass  to 
'he  lever  L.  From  the  same  lever  hangs  a  cord  of  twisted 
silk,  C  C,  to  which  is  suspended  a  leaden  ball. 

Let  us  suppose  the  ball  to  be  at  its  lowest  position — at 
the  point  A — the  lever  L  occupies  the  place  marked  by  a  dotted 
line,  while  in  the  registering  instrument  the  air  driven  out 
raises  the  lever  L',  which  traces  the  movement. 


MOVEMENTS  OF  THE  WINGS  OF  BIRDS.  245 


Now  let  us  raise  the  ball  to  the  position  B ;  the  elasticity 
of  the  india-rubber  thread  will  cause  the  lever  to  rise.  Thus 
it  is  acted_upon  alternately  by  two  forces,  sometimes  by  the 
traction  exerted  by  the  silk  thread,  which  lowers  it ;  at  others, 
by  the  retraction  of  the  india-rubber,  which  re-acts  as  soon  as 
the  tractile  force  ceases.  Thus  the  lever  will  follow  faithfully 
all  the  movements  which  are  given  to  the  extremity  of  the 
thread  which  draws  it  down. 


Fio.  102  —  Transmission  of  a  to-and-fro  movement  by  means  of  a  simple 
traction-cord. 


The  lever  I/,  which  is  to  trace  on  the  cylinder  the  move- 
ments transmitted  to  it,  moves  in  an  opposite  direction  to  the 
course  of  the  cord  C  C.  The  tracing  will  thus  be  reversed, 
and  if  it  were  important  to  obtain  it  in  the  same  direction,  it 
would  be  necessary  to  turn  the  registering  drum,  so  as  to  place 
the  membrane  downwards.* 

With  two  instruments  of  this  kind,  one  acted  upon  by  the 

*  As  many  instruments  of  this  kind  are  required  as  there  are  move- 
ments to  be  studied.  But  three  connected  levers  will  always  be  sufficient 
to  ascertain  the  movements  of  a  point  in  space,  since  each  of  the  posi- 
tions of  this  point  is  defined  when  it  has  been  determined  with  reference 
to  three  axes  at  right  angles  to  each  other. 
23 


246 


ANIMAL  MECHANISM. 


vertical  tractions  of  a  thread  attached  to  the  wing  of  the  hird, 
and  the  other  by  the  horizontal  tractile  force  of  a  second 
thread  also  fastened  to  its  wing,  we  can  verify  the  experiment 
which  has  furnished  us  with  the  trajectory  of  this  organ,  and 
obtain  with  much  greater  accuracy  the  curve  illustrating  its 
movements.  This  we  have  perfectly  succeeded  in  doing,  as 
we  shall  show  further  on. 

But  this  is  not  all  that  we  wished  to  obtain.  We  might 
have  made  the  bird  carry  the  apparatus  which  we  have  just 
described,  and  put  it  in  communication  with  the  registers  by 
means  of  tubes,  as  in  the  experiment  represented  in  fig.  99. 
But  while  seeking  to  render  the  analogies  of  the  movements 
of  flight  perfect,  we  wished  also  to  discover  a  plan  which 
would  be  equally  applicable  to  the  living  bird,  and  to  every 
kind  of  machine  intended  to  represent  artificially  aerial  loco- 
motion. 

In  this  project  we  must  endeavour  to  copy  Nature  in  her 
functions,  as  the  artist  does  in  her  form.  We  must  give  more 
rapidity  to  movements  which  are  too  slow,  and  render  those 
slower  which  are  too  rapid,  until  they  have  absolutely  the  same 
characters  and  the  same  mechanical  effects  as  those  of  the 
bird. 

This  incessant  comparison  requires  us  to  place  ourselves 
under  new  conditions.  Hitherto,  our  analytical  studies  have 
been  directed  to  a  bird  flying  at  liberty ;  for  since  we  have 
never  been  able  to  imitate  flight  exactly  by  mechanical 
methods,  it  would  be  impossible  to  leave  an  artificial  instru- 
ment to  itself;  it  would  be  broken  at  each  experiment. 

The  comparison  of  the  movements  of  the  bird  with  those 
of  imitative  instruments  does  not  require  these  movements  to 
be  effected  under  the  conditions  of  free  flight.  Provided  that 
the  bird,  although  restrained  in  its  movements,  should  flap 
its  wings  with  the  intention  of  flying,  we  shall  be  able  to 
study  these  muscular  actions  with  reference  to  their  characters 
of  force,  extent,  and  duration.  A  bird  suspended  by  a  cord 
and  allowed  to  flap  its  wings  might,  for  example,  be  com- 
pared with  an  artificial  apparatus  suspended  in  the  same 
manner. 

We  have  tried  a  less  imperfect  mode  of  suspension  which 


MOVEMENTS  OF  THE  WINGS  OF  BIRDS.  217 


allows  the  bird  to  fly  under  conditions  almost  normal,  and 
at  the  same  time  will  permit  the  artificial  instruments  to  make 
attempts  at  flight,  without  any  fear  of  letting  them  fall,  if 
the  movements  which  they  produce  should  be  insufficient  to 
sustain  them  in  the  air.  We  will  now  describe  this  suspen- 
sory apparatus. 

There  is  a  sort  of  frame-work  of  six  or  seven  metres  in 
diameter,  in  which  the  bird  moves  continuously,  being  thus 
able  to  furnish  us  with  an  observation  of  a  circular  flight  of 
long  duration.  We  give  the  instrument  a  large  radius,  that 
its  curve,  being  less  abrupt,  should  modify  less  the  nature  of 
the  movement  which  the  bird  may  make.  Harnessed  to  some 
extent  to  the  extremity  of  a  long  arm  which  turns  on  a  central 
pivot,  the  bird  ought  to  be  as  free  as  possible  to  go  through 
its  movements  of  vertical  oscillation.  We  shall  presently  see 
that  a  bird  passes  through  a  double  oscillatory  movement  in 
a  vertical  plane  for  each  revolution  of  its  wings. 

Arrangement  of  the  frame. — The  conditions  to  be  fulfilled  are 
the  following :  in  the  first  place,  a  great  mobility  of  the 
instrument,  that  the  bird  may  have  the  least  possible  resist- 
ance to  overcome  in  its  flight ;  then,  a  perfect  rigidity  of  the 
arm  of  the  machine,  to  prevent  any  vibrations  peculiar  to 
itself,  which  might  render  unnatural  the  movements  executed 
by  the  bird. 

Fig.  103  shows  the  general  arrangement  of  the  apparatus. 
A  steel  pivot,  resting  on  a  solidly-cast  socket  of  great  weight, 
is  placed  on  the  platform  of  a  photographic  table.  This  table 
is  raised  by  means,  of  rack-work,  so  that  the  operator,  after 
having  arranged  his  apparatus  so  as  to  suit  the  experiment, 
may  place  the  platform  sufficiently  high  for  the  instrument  to 
turn  freely  above  his  head. 

The  frame- work,  properly  so  called,  is  a  bow  formed  of  a 
long  piece  of  fir-wood  slightly  curved.  The  string  of  this 
bow  is  an  iron  wire,  which  is  fixed  by  the  middle  to  a  cage 
of  wood  traversed  by  the  central  pivot.  Care  is  taken  to 
balance  the  two  ends  of  the  apparatus,  by  gradually  adding 
weights  to  the  arm  not  carryiug  the  bird  which  is  the  subject 
of  the  experiment. 

If  we  did  not  take  this  precaution,  the  apparatus,  as  it 


MOVEMENTS  OF  THE  WINGS  OF  BIRDS.  24y 


turns,  would  give  lateral  movements  to  the  pivot  on  which  it 
rests,  and  to  the  base  itself. 

To  furnish  the  bird  with  a  solid  point  of  suspension,  pro- 
tected not  only  from  vertical  oscillations,  but  from  move- 
ments of  torsion,  we  have  placed  at  each  end  of  the  instrument 
a  cross  piece  of  wood,  to  the  two  extremities  of  which  are 
attached  cords  communicating  with  the  ceiling  of  the  room. 
At  this  point  is  a  revolving  hook,  which  turns  freely  with  the 
machine. 

Of  the  apparatus  which  suspends  the  bird. — Fig.  104  shows 
the  details  of  this  suspension  which  binds  the  bird  to  the  arm 
of  the  instrument,  while  it  confines  as  little  as  possible  the 
liberty  of  its  movements. 

Of  the  registering  apparatus. — The  transmitting  tubes  are 
arranged  along  the  arm  of  the  instrument ;  they  are  fastened 
to  it  throughout  all  its  length,  and  end  in  a  register  which 
carries  three  lever-drums  tracing  on  the  revolving  cylinder. 
The  instrument  in  its  rotation  would  cause  the  transmitting 
tubes  to  roll  round  its  axis,  if  the  register  to  which  they  are 
directed  did  not  participate  in  the  general  rotation. 

We  see  in  fig.  103  how  this  apparatus  is  arranged.  The 
cylinder  is  placed  vertically  above  the  axis  of  the  instrument ; 
the  three  levers  trace  upon  it.  The  whole  apparatus  rests 
on  a  tablet,  which  turns  on  the  central  pivot.  We  have  here 
well-known  arrangements,  in  which  several  movements  are 
registered  at  the  same  time  on  the  cylinder ;  it  will,  there- 
fore, be  useless  to  repeat  the  precautions  which  are  to  be 
taken  in  the  management  of  the  apparatus,  such  as  the  exact 
superposition  of  the  tracing  points,  &c. 

The  movements  of  the  wing  are  extremely  rapid ;  they  can 
be  registered  only  on  a  cylinder  turning  with  great  velocity  ; 
that  which  is  employed  in  this  experiment  makes  one  revolu- 
tion in  a  second  and  a  half.  The  shortness  of  the  time  at 
our  disposal  to  trace  the  movements  of  the  bird  compel  us  to 
do  so  only  at  the  precise  moment  when  the  phenomena  which 
we  wish  to  observe  are  presented,  whether  it  be  the  swiftest 
flight,  the  gradual  slackening  of  its  speed,  or  the  efforts 
made  at  starting.  If  the  three  levers  were  to  rub  constantly 
on  the  cylinder,  we  should  soon  have  nothing  but  a  confused 


ANIMAL  MECHANISM, 

in 


MOVEMENTS  OF  THE  WINGS  OF  BIRDS.  251 


scrawl.  It  is  indispensably  necessary  so  to  arrange  tlie 
instrument  that  the  points  of  the  levers  should  touch  the 
cylinder  only  at  the  moment  when  we  wish  to  register  the 
phenomena,  and  to  cease  this  contact  after  one,  or  at  most 
two  revolutions  of  the  cylinder,  in  order  to  avoid  confusion  in 
the  tracings. 

We  have  recourse,  for  this  purpose,  to  the  arrangements 
already  made  in  our  experiments  upon  walkiDg. 

Fig.  103  shows  the  experimenter  at  the  instant  when  he 
is  about  to  take  a  tracing  from  the  pigeon.  Observing  the 
flight  of  the  bird,  he  seizes  the  moment  when  it  becomes 
regular,  and  squeezes  the  india-rubber  ball.  The  contact  of 
the  levers  is  immediately  produced,  and  the  tracing  is  made. 
After  a  second  and  a  half  he  ceases  to  press  it,  the  spring 
removes  the  levers  from  the  cylinder,  and  the  tracing  is  over. 

With  a  little  practice  it  is  very  easy  to  ascertain  the  dura- 
tion of  the  revolution  of  the  cylinder,  and  to  confine  the 
tracing  to  the  necessary  length. 

This  long  description  was  necessary,  as  we  were  anxious 
to  make  this  apparatus  understood,  it  being  the  most  im- 
portant of  all,  on  account  of  its  double  function.  We  shall 
have  to  employ  it,  not  only  in  the  analytical,  but  also  in  the 
synthetical  part  of  these  studies,  when  we  shall  attempt  to 
represent  the  movements  in  the  bird's  flight. 

New  determination  of  the  trajectory  of  a  bird's  wing. — A 
pigeon  was  made  use  of  in  this  experiment.  It  was  a  male 
bird  of  the  variety  called  the  Roman  pigeon,  very  vigorous, 
and  accustomed  to  fly.*  Fig.  104  shows  the  arrangement  of 
the  apparatus  which  we  have  used  for  the  purpose  of  study- 
ing its  movements. 

It  is  more  especially  to  the  humerus  that  we  have  directed 
our  attention,  in  order  to  obtain  the  movements  of  the  wing  in 
space.  For  this  purpose  a  wire  is  twisted  round  the  bone, 
holding  it  as  in  a  ring,  and  furnishing  by  its  free  ends  a  firm 
point  of  attachment  outside  the  wing  for  other  wires  w  hich 
act  on  the  experimental  drums. 

*  This  latter  point  is  of  great  importance,  for  the  greater  part  of  the 
birds  in  a  dove-cot  are  of  no  use  to  us,  on  account  of  their  inexperience  in 
flight. 


252 


ANIMAL  MECHANISM. 


The  movements  of  the  two  wings  being  perfectly  symme- 
trical in  regular  flight,  we  cause  two  wires,  which  pass  sym- 
metrically from  the  wings,  to  converge  to  each  of  the  experi- 
mental drums.  Thus,  drum  No.  1,  intended  to  give  signals 
of  the  elevation  and  depression  of  the  wing,  receives  two 
wires,  each  of  which  proceeds  from  one  of  the  humerus  bones 
of  the  pigeon,  at  about  3  centimetres  outside  the  articulation 
of  the  shoulder.  These  wires  rise  and  converge,  and  are 
attached  to  the  point  of  the  lever  No.  1 ;  while  from  the 
same  point  proceeds  an  india-rubber  thread,*  which  serves  as 
a  counter- spring,  and  rises  vertically  to  a  hook  above,  which 
holds  it. 

We  have  before  seen  (fig.  102)  how  the  lever  of  the 
experimental  drum  receives,  under  these  conditions,  all  the 
movements  of  elevation  and  depression  executed  by  the 
humerus  of  the  bird. 

Two  other  wires,  each  attached  to  the  humerus  of  the 
pigeon  on  each  wing,  and  starting  from  the  same  point  of  the 
bone  to  which  were  fastened  the  wires  of  drum  No.  1,  con- 
verge also,  turning  backwards,  and  proceed  to  the  lever  of 
drum  No.  2.  This  is  the  drum  which  receives  the  movements 
executed  by  the  wing  in  the  antero-posterior  direction.  The 
two  drums  send  their  signals  by  air  tubes  to  the  register 
situated  in  the  centre  of  the  apparatus. 

Experiment. — After  having  ascertained  that  the  two  levers 
intended  to  trace  have  their  points  situated  on  the  same 
vertical,  the  pigeon  is  allowed  to  fly.  The  bird  goes  through 
the  movements  of  flight,  and  soon  carries  round  with  con- 
siderable rapidity  the  instrument  to  which  it  is  attached. 
The  operator,  placed  in  the  centre  of  the  apparatus,  has  only 
to  follow  for  a  few  paces  the  rotation  of  the  instrument. 
During  this  time  he  holds  in  his  hand  the  india-rubber  ball, 
and  has  only  to  compress  it,  in  order  that  the  two  levers  may 
rest  with  their  points  against  the  blackened  paper,  and  that 
the  tracing  may  commence.  As  soon  as  the  flight  is  well 
established,  and  seems  to  be  carried  on  under  satisfactory 

*  In  fig.  104  a  spir  spring  has  been  substituted  for  this  india-rubber 
thread. 


MOVEMENTS  OF  THE  WINGS  OF  BIRDS.  253 

conditions,  he  compresses  the  ball,  and  produces  the  tracing 
represented  in  fig.  105. 


A 


Fio.  105.— Tracing  of  the  movements  of  a  pigeon's  wing.  The  upper  line, 
A  P,  shows  the  movements  forwards  and  backwards.  The  lowt  r  line 
U  B,  the  movements  up  and  down. 

Interpretation  of  the  tracings. — The  curves  are  read  from  left 
to  right,  like  ordinary  writing.  The  upper  curve  is  that 
described  by  the  humerus  of  a  bird  in  its  movements  for- 
wards and  backwards  ;  the  direction  of  these  movements  is 
indicated  by  the  letters  A  and  P,  which  signify  that  all  the 
tops  of  the  curves,  as  well  as  that  at  A,  correspond  with  the 
time  when  the  wing  has  reached  the  most  forward  part  of  its 
course ;  the  lower  parts  of  the  curves,  on  the  contrary,  indicate, 
as  well  as  that  at  the  point  P,  the  moment  when  the  wing 
has  reached  the  hinder  part  of  its  movement. 

The  horizontal  line  which  cuts  this  curve  has  been  traced 
in  a  previous  experiment  by  the  point  of  the  lever  at  the 
instant  when  the  wings  of  the  bird,  kept  motionless  by  an 


254 


ANIMAL  MECHANISM. 


assistant,  may  be  considered  as  horizontally  extended,  tending 
neither  forwards  nor  backwards.  This  line  represents,  there- 
fore, to  some  extent,  the  zero  of  the  scale  of  the  movements 
of  the  wing  in  its  an tero -posterior  direction.  The  inspection 
of  the  curve  shows  us  also,  that  the  pigeon's  wing  was  carried 
more  especially  in  the  direction  of  the  upper  parts,  similar  to 
the  point  A ;  in  other  terms,  that  the  forward  predominated 
over  the  backward  movement. 


Fig.  106. — Superposition  of  the  preceding  curves  on  paper  divided  in 'milli- 
metres. The  two  curves  have  a  common  direction  with  reference  to  the 
axis  of  the  abscissae. 


The  same  explanations  would  apply  to  the  lower  curve 
H  P,  which  expresses  the  movements  of  the  wing  upwards 
and  downwards. 

In  order  to  ascertain  if  the  course  of  the  pigeon's  wing  in 
the  present  experiment  is  apparently  the  same  as  that  of  the 
buzzard  recorded  before,  we  have  constructed  the  complete 
curve  of  the  wing  during  one  of  its  revolutions,  making  use 
for  this  purpose  of  the  two  partial  curves  of  fig.  105. 

The  following  is  the  method  employed  in  this  construction  : 

In  order  to  give  more  facility  to  the  measurement  of  the 
positions  of  the  different  points  of  these  curves,  we  have 
copied  them  both  on  a  paper  graduated  in  centimetres  and 


MOVEMENTS  OF  THE  WINGS  OF  BIRDS.  255 


millimetres.  We  have  traced  in  full  line  one  of  these  curves, 
that  of  the  movements  in  the  antero -posterior  direction,  the 
course  of  which  is  indicated  by  the  letters  A  and  P ;  then  we 
have  represented,  by  a  dotted  line,  the  curve  of  the  upward 
and  downward  motions  with  the  letters  H  and  B.  We  have 
placed  these  two  tracings  over  each  other,  so  as  to  make  the 
zero-lines  of  each  coincide.  We  have  also  taken  care  to 
preserve  the  vertical  superposition  of  the  corresponding  points 
of  each  of  these  curves  ;  we  may  therefore  be  certain  that, 
wherever  any  vertical  line  cuts  the  two  curves,  the  inter- 
sections correspond  with  the  position  which  the  humerus  of 
the  bird  occupies,  at  that  instant,  with  reference  to  two  planes 
at  right  angles  to  each  other.  The  intersection  with  the  dotted 
line  will  express,  by  the  length  of  the  ordinate  drawn  from 
this  point  to  the  axis  of  the  abscissa?,  the  position  which  the 
wing  then  occupies  with  reference  to  an  horizontal  plane ;  the 
intersection  with  the  full  line  will  express  the  position  of  the 
wing  as  referred  to  a  vertical  plane. 

This  determination  is  realised  in  fig.  107  for  the  trajectory 
of  the  wing,  which  has  been  constructed  by  successive  points 
in  the  following  manner: — 


256 


ANIMAL  MECHANISM. 


Let  there  be  two  lines,  x  x,  forming  the  axis  of  tho 
abscissae,  and  y  y  that  of  the  ordinates.  Let  us  assume,  that 
all  which  is  above  the  line  of  zeros,  in  the  full  curve — that  is 
to  say,  that  which  corresponds  with  a  movement  in  a  forward 
direction,  ought  to  point  to  the  right  of  the  line  y  y.  In- 
versely, that  all  which  is  below  the  zeros,  in  the  full  curve, 
will  point  to  the  left  of  the  axis  of  y  y.  The  position  with 
reference  to  this  axis  will  be  reckoned,  parallel  to  it,  by 
menns  of  millimetric  divisions. 

On  the  other  hand,  the  different  measurements  taken  on 
the  dotted  curve  (that  which  expresses  the  upward  motion  of 
the  wiug)  must  point  to  the  corresponding  elevation,  reckoned 
above  or  below  the  line  x  x,  according  as  these  points  in  the 
curve  of  the  elevations  are  removed  a  certain  number  of 
millimetres  either  above  or  below  the  zero  line. 

Let  us  take  as  our  point  of  departure,  in  the  construction 
of  the  new  curve,  the  point  c  (fig.  107),  chosen  on  the  dotted 
line,  at  one  of  the  times  when  the  wing  has  arrived  at  one  of 
its  anterior  limits. 

This  point,  according  to  the  millimetric  scale,  shows  us 
that  the  wing  is  depressed  1 3  divisions  beneath  the  horizontal 
line.  Let  us  follow  the  vertical  line  which  passes  through 
the  point  c,  till  it  meets  with  the  curve  of  movement  in  the 
antero-posterior  direction:  the  intersection  of  this  vertical 
line  with  the  curve  shows  us  that  the  wing  at  this  moment 
had  been  carried  forward  26  divisions;  on  the  new  curve, 
therefore,  the  point  a  ought  to  be  marked  at  a  well-ascertained 
position  c,  which  will  be  found  at  the  intersection  of  the  thir- 
teenth division  below  the  axis  x  x,  with  the  twenty- sixth  to  the 
right  of  the  axis  y  y,  which  according  to  what  we  have  as- 
sumed, corresponds  with  26  divisions  in  the  forward  direction. 

To  determine  a  second  point  in  our  curve,  let  us  proceed, 
in  reading  the  tracings,  one  millimetric  division  farther  to 
the  right ;  we  shall  find,  as  before,  the  intersection  of  the 
vertical  at  this  point  with  the  two  curves,  and  we  shall  thus 
have  a  second  point  in  the  new  construction  determined. 

The  series  of  successive  points  obtained  in  this  manner 
form  a  curve  which  shows  the  course  of  the  wing,  the  arrow 
indicates  the  direction  of  the  movement. 


CHANGES  IN  THE  PLANE  OF  THE  BIRD'S  WING.  257 


By  constructing  thus  the  whole  figure,  we  see  that  this 
curve,  after  proceeding  downwards  and  forwards,  rises  and 
returns  back  again. 

By  comparing  this  figure  with  that  which  we  have  obtained 
by  means  of  another  apparatus  (fig  100),  on  another  kind  of 
bird,  aud  by  examining  the  movement  of  another  part  of  the 
wing,  we  shall  find  striking  resemblances  between  the  two 
curves,  which  show  that  birds  proceed  in  their  flight  by 
movements  which  are  almost  identical.  In  fact,  the  bone  of 
the  wing  in  each  describes  a  kind  of  irregular  ellipse,  with 
its  greater  axis  inclined  downward  and  forward.  The  im- 
portance of  this  determination  is  so  great,  that  we  trust  we 
shall  be  pardoned  for  the  long  and  minute  details  of  the 
experiments  which  have  furnished  these  results. 

OF   THE   CHANGES  IN  THE   PLANE   OF  THE  WING. 

We  have  seen  in  Chapter  I.  that  the  wing  of  the  insect  is 
subject  to  torsions  under  the  influence  of  the  resistance  of  the 
air,  and  that  the  inclination  of  the  plane  of  its  wing  is 
changed  at  every  moment.  These  movements,  which  are 
entirely  passive,  constitute  the  essence  of  the  mechanism  of  the 
insect's  flight;  the  wing,  in  each  of  its  alternate  movements, 
acts  on  the  resistance  of  the  air,  and  gains  from  it  a  force 
which  is  exerted  on  the  membrane  by  the  side  of  the  main- 
rib,  thus  serving  to  sustain  the  insect  and  propel  it  forward. 
The  structure  of  the  bird's  wing  does  not  allow  the  existence 
of  a  similar  mechanism.  Its  wing  during  its  ascent  does  not 
present  to  the  air  a  resisting  plane,  because  the  feathers  which 
fold  over  each  other  would  open  to  allow  it  to  pass  through. 
The  deprt  ssion  of  the  wing  is  therefore  the  only  phase  in  the 
flight  of  the  bird  which  has  any  analogy  with  that  of  the 
insect.  Besides,  the  curve  described  by  the  point  of  the  bird's 
wing  is  sufficiently  different  from  that  of  the  insect,  to  prove 
that  their  mechanical  conditions  are  very  dissimilar. 

It  was  indispensable  to  determine  by  experiment  the  dif- 
ferent inclinations  of  the  plane  of  the  bird's  wing  at  each 
phase  of  its  revolutions.  In  fact,  to  estimate  the  resistance 
which  the  air  presents  at  each  moment  of  the  flight,  we  must 
know  the  two  elements  of  this  resistance :  first,  the  angle 
24 


258 


ANIMAL  MECHANISM. 


under  which  the  plane  of  the  wing  strikes  the  air,  and 
secondly,  the  velocity  with  which  it  is  lowered.  Nothing  is 
more  easy  than  to  obtain  the  second  data  of  the  problem ; 
we  can  reduce  them  from  the  curve  which  represents  the 
position  of  the  wing  at  each  instant,  a  curve  of  which  we 
have  an  example  in  fig.  108,  as  obtained  from  a  pigeon.  But 
the  difficulty  which  presents  itself,  is  to  obtain  the  indication 
of  the  changes  which  take  place  in  the  plane  of  the  wing 
during  flight.  For  this  purpose  we  have  had  recourse  to  the 
following  mechanism. 

We  have  seen,  in  fig.  99,  that  a  rod  connected  with  a 
Cardan  universal  joint,  whose  centre  of  rotation  is  near  the 
scapulo-humeral  articulation,  can  be  made  to  represent  ac- 
curately the  circular  movements  of  the  wing.  But  Cardan's 
joint,  though  it  obeys  the  rotary  motions  of  every  kind  which 
are  given  to  the  rod,  does  not  allow  any  movements  of  torsion 
with  reference  to  the  axis  of  this  rod. 


/  j 

Fig.  108. — Theoretical  figure  of  the  apparatus  to  investigate  the  torsion  of 
the  wing. 


Let  fig.  108  be  a  kind  of  apparatus  of  this  sort:  we  can 
give  the  rod  t  t  every  kind  of  motion  in  the  vertical  or  hori- 
zontal direction ;  it  will  follow  all  the  impulses  which  it 
receives.  But  if  we  take  hold  of  the  extremity  of  the  rod, 
near  the  lever  I  which  is  perpendicular  to  it,  and  try  to  give 
the  lever  a  movement  of  torsion,  as  if  we  were  turning  a  screw, 
the  Cardan  does  not  allow  this  movement  to  be  made,  and  the 
rod  resists  the  impulse  brought  to  bear  upon  it.  Let  us 
suppose  that  behind  the  Cardan  joint,  and  on  the  prolonga- 
tion of  the  rod  t  i,  there  is  another  cylindrical  rod,  p,  turning 
in  a  tube ;  this  rod  will  turn  under  the  influence  of  the  torsion 
exercised  by  the  hand  holding  the  lever  I,  and  if  the  rod  p 
carries  a  lever     at  right  angles  to  it,  and  situated  in  the 


CHANGES  IN  THE  PLANE  OF  THE  BIRD'S  WING.  259 


some  plane  as  I,  we  shall  see  that  these  levers  correspond 
with  each  other,  and  that  every  change  of  plane  undergone  by 
the  first  will  be  transmitted  to  the  second. 

Under  these  conditions,  if  we  cause  the  lever  I  to  signal  the 
changes  of  plane  which  the  wing  undergoes  in  the  various 
phases  of  its  revolution,  these  changes  will  be  communicated 
to  the  lever  V,  which  can  in  its  turn  act  on  an  experimental 
apparatus,  and  transmit  the  signal  under  the  form  of  a 
tracing.  This  is  precisely  the  method  which  we  have  em- 
ployed in  our  experiments.  The  lever  I  was  placed  upon  the 
wing  of  the  bird,  and  was  held  in  a  horizontal  position. 
The  lever  Vt  also  horizontal,  was  fastened  by  a  wire  to  the 
lever  of  an  experimental  drum  placed  above  it,  and  arranged 
in  the  same  manner  as  in  the  experiments  described  in  the 
former  chapter. 

When  we  caused  the  plane  of  the  wing  to  oscillate,  so  as 
to  turn  its  upper  surface  more  or  less  backw  ards,  the  registered 
curve  was  depressed ;  it  rose,  on  the  contrary,  when  we  turned 
the  wing  so  as  to  carry  its  upper  surface  forwards. 

Still  a  difficulty  presented  itself.  It  was  not  possible  to  fix 
the  lever  I  at  one  point  of  the  rod  1 1 ;  and,  at  the  same  time, 
to  render  it  immovable  at  a  single  point  in  the  bird's  wing. 
In  fact,  the  Cardan  joint,  not  having  the  same  centre  of  motion 
as  the  articulation  of  the  wing,  it  followed  that  in  the  vertical 
movements  the  rod  slipped  upon  the  wing.  It  was  necessary, 
therefore,  for  the  lever  I,  while  fixed  to  the  feathers  of  the 
bird,  to  glide  freely  on  the  rod  in  the  direction  of  its  length, 
and  yet  that  it  should  cause  it  to  receive,  under  the  form  of 
torsion,  all  the  changes  of  inclination  that  are  transmitted  to 
it  by  the  wings  of  the  bird.  We  see  in  ft*.  109  how  this 
result  has  been  obtained. 

Let  1 1  be  the  rod  which  is  to  follow  all  the  circular  move- 
ments executed  by  the  bird.  This  rod  has  in  it  deep 
longitudinal  grooves,  which  give  its  section  the  appearance  ot 
a  star ;  it  glides  freely  in  a  tube  which  is  applied  to  its 
external  surface.  But  at  one  of  the  extremities  of  the  tube  is 
a  metallic  sliding  casting,  the  interior  part  of  which  is  grooved 
like  a  star,  through  which  passes  the  rod  whose  grooves  slide 
in  those  of  the  star-shaped  opening.    Then  the  lever  /  is 


260 


ANIMAL  MECHANISM. 


soldered  to  this  tube,  and  is  able  to  move  with  it  to  any  point 
along  the  rod,  thus  allowing  full  liberty  to  the  movements  of 
flight,  while  no  change  of  plane  can  be  effected  without  com- 
municating a  movement  of  torsion  to  the  rod. 

After  some  experiments,  it  became  necessary  to  make  im- 
provements in  this  apparatus.  Thus,  the  lever  I  had  a  tendency 
to  get  twisted  on  account  of  the  displacement  of  the  feathers 
during  flight;  it  was  replaced  (fig.  109)  by  a  piece  with  three 


Fig.  109. — Actual  arrangement  of  the  apparatus  intended  to  experiment 
upon  the  movements  of  the  wing,  and  its  change  of  plane. 

movable  levers,  b  b  b,  turning  in  the  same  plane  round  a 
common  centre,  like  the  blades  of  a  fan.  Each  of  these  little 
branches  terminated  in  a  hook.  After  having  attached  the 
sliding  tube  to  the  false  wing  of  the  bird,  the  extremity  of 
each  of  these  three  blades  was  tied  to  one  of  the  long  feathers 
of  the  wing.  This  ligature,  made  with  india-rubber,  gave 
excellent  results. 

The  lever  I  (fig.  109)  was  also  defective  on  account  of  its 
unequal  action.  In  its  stead  was  substituted  a  pulley  of  short 
radius,  placed  on  the  rod  prolonged  behind  the  Cardan  joint. 
The  thin  cord  r  r,  which  was  to  transmit  the  torsions  of  the  rod, 
passed  round  the  wheel  of  this  pulley.  In  this  manner  the 
rotation  of  the  pulley,  resulting  from  the  torsion  of  the  rod, 
always  faithfully  transmitted  this  torsion  to  the  experimental 
lever. 

To  put  an  end  to  this  long  description  of  the  instrument 
intended  to  transmit  the  signals  of  the  elevation  and  depression 
of  the  wing,  let  us  only  say  that  the  piece  situated  at  the  base 
of  the  lever  t  t  is  intended  to  transmit  the  vertical  and 


CHANGES  IN  THE  PLANE  OF  THE  BIRD'S  WING.  261 


horizontal  movements  by  two  systems  of  cords.  For  the 
vertical  ones,  a  cord  v  goes  to  the  lever  of  the  experimental 
drum.  The  cord  h  transmits  to  another  apparatus  the 
movements  in  the  horizontal,  that  is,  in  the  antero  posterior 
direction. 

Experiment. —  A  buzzard  to  which  this  apparatus  has  been 
adapted  is  harnessed  to  the  instrument  and  allowed  to  fly :  we 
obtain  at  the  same  time  the  three  curves  represented  in 
fig.  110.  With  these  three  data,  we  can  construct,  not  only  the 
trajectory  of  the  wing,  but  the  series  of  inclinations  of  its  plane 
at  the  different  points  of  its  course. 

The  curve  traced  with  a  full  line  corresponds  with  the 
movements  of  the  wing  in  an  antero -posterior  direction.  The 
point  A,  and  those  homologous  with  it,  correspond  with  the 
extreme  anterior  position  of  the  wing  ;  the  point  P  with  the 
extreme  posterior  position.  The  curve  formed  of  interrupted 
strokes  indicates  the  relative  height  of  the  wing  in  space ;  the 
point  H  corresponds  with  the  maximum  elevation  of  the  wing, 
and  the  point  B  with  its  greatest  depression. 

These  two  first  curves  enable  us  to  construct,  by  means  of 
points,  the  closed  curve*  (fig.  Ill)  representing  the  trajectory 
of  the  buzzard's  wing.  It  is  by  this  trajectory  that  we  shall 
determine  the  inclination  of  the  plane  of  the  wing  at  every 
part  of  its  elliptical  course. 

For  this  purpose,  we  must  return  (fig.  110)  to  the  dotted 
curve  S,  which  is  the  expression  of  the  torsions  of  the  wiug  at 
different  instants.  The  positive  and  negative  ordinates  of  this 
curve  correspond  with  the  trigonometrical  tangents  of  the 
anglesf  which  the  wing  makes  with  the  axis  of  the  body. J: 

*  This  curve  is  not  always  closed  ;  this  is  the  case  only  when  the  flight 
Is  extremely  regular. 

+  "We  must  subtract  algebraically  from  the  angle  found,  a  constant 
quantity,  the  angle  of  30°  which  the  wing,  during  repose,  makes  with  the 
horizon. 

X  We  cannot  positively  affirm  that  this  axis  is  horizontal  ;  it  seems 
rather  that  it  is  inclined  so  that  the  beak  of  the  bird  turns  slightly 
upwards.  This  inclination  of  the  axis  would  necessitate  a  correction  in 
the  absolute  inclinations  of  the  wing  at  the  different  points  of  its 
revolution. 


262  ANIMAL  MECHANISM. 

They  enable  us,  therefore,  to  trace  in  fig.  111a  series  of 
lines,  each  of  which  expresses,  by  its  inclination  with  respect 

3  i 

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to  the  horizontal  axis,  that  which  the  plane  of  the  wing 
presented  to  the  horizon  at  this  same  portion  of  its  course. 


CHANGES  IN  THE  PLANE  OF  THE  BIRD'S  WING.  263 


The  direction  of  the  movement  of  the  wing  is  read  from  above 
and  forward,  from  H  to  Av. 

Fig.  Ill  shows  that  the  wing  during  its  ascent  assumes 
an  inclined  position  which  allows  it  to  cut  the  air  so  as  to 
meet  with  the  minimum  of  resistance  ;  while  in  its  descent, 
on  the  contrary,  the  position  of  its  plane  is  reversed,  so  that 
its  lower  surface  turns  downwards  and  slightly  backwards. 
It  follows,  that  in  its  period  of  depression,  the  wing,  by  its 
obliquity,  acts  upon  the  resistance  of  the  air,  and  while  raising 
the  body  of  the  bird,  carries  it  forward.    We  see,  also,  that 


Fig.  111.— Inclinations  of  the  plane  of  the  wing  with  reference  to  the  axis 
(Av)  of  the  body  during  flight 


the  inclination  of  the  winj*  changes  gradually,  in  the  different 
phases  of  its  elevation  and  of  its  descent.  Especially  in  this 
latter  phase,  the  influence  of  the  air  in  shaping  the  course  of 
the  wing  is  more  evidently  seen ;  it  is,  in  fact,  at  the  moment 
when  the  rapidity  of  its  depression  attains  its  maximum  that 
we  see  the  posterior  edge  of  the  wing  turn  up  the  more  strongly. 

The  wing,  when  it  has  reached  the  end  of  its  descending 
course,  changes  its  plane  very  suddenly.  The  explanation  of 
this  movement  is  very  natural.  As  soon  as  the  resistance  of 
the  air  ceases  to  raise  the  feathers,  these,  by  their  elasticity, 
return  to  their  ordinary  position,  which  they  occupy  during  all 
the  phase  of  elevation. 

Even  the  ellipse  which  forms  the  trajectory  of  the  wing  can 


264 


ANIMAL  MECHANISM. 


be  explained  by  the  resistance  of  the  air.  The  muscular 
apparatus  of  the  bird,  like  that  of  the  insect,  has  nothing  to 
do  with  the  course  of  the  wing ;  elevation  and  depression  are 
almost  all  the  movements  that  it  can  produce.  But  the 
resistance  of  the  air  during  the  phase  of  descent  gives  rise  to 
the  anterior  convexity  of  the  curve  passed  through,  by  means 
of  a  mechanism  which  we  already  understand.  The  posterior 
convexity  which  belongs  to  the  ascensional  phase  is  also 
explained  by  the  action  of  the  air  on  the  lower  surface  of  the 
wing,  which  it  carries  backward  at  the  same  time  as  it  raises 
it.  We  must  seek  for  the  demonstration  of  this  theory  in  the 
artificial  representation  of  these  different  movements. 


CHAPTER  VI. 

RE- ACTIONS  OF  THE  MOVEMENTS  OF  THE  WING  ON  THE 
BODY  OF  THE  BIRD. 

Re-actions  of  the  movements  of  the  wing— Vertical  re-actions  in  different 
species  ;  horizontal  re -actions  or  changes  in  the  rapidity  of  flight ; 
simultaneous  study  of  the  two  orders  of  re-actions — Theory  of  the 
flight  of  the  bird— Passive  and  active  parts  of  the  wing — Reproduc- 
tion of  the  mechanism  of  the  flight  of  the  bird. 

In  order  that  we  may  follow,  in  studying  the  flight  of  the 
bird,  the  same  plan  which  has  guided  our  researches  on  the 
other  kinds  of  locomotion,  we  must  determine  what  are  the 
reactionary  effects  of  each  of  the  movements  of  the  wing  on 
the  body  of  the  animal. 

Two  distinct  effects  are  produced  during  flight :  by  one,  the 
bird  is  sustained  in  opposition  to  its  weight ;  by  the  other,  it 
is  subjected  to  a  propulsive  force  which  carries  it  from  one 
place'  to  another.  But  do  we  find  that  the  bird,  when  sus- 
tained in  the  air,  keeps  at  a  constant  level,  or  does  it  pass 
through  oscillations  in  the  vertical  plane  ?  Does  it  not 
experience,  by  the  intermittent  effect  of  the  flapping  of  its 
wings,  rising  and  falling  motions,  of  which  the  eye  can  detect 


RE- ACTIONS  DURING  FLIGHT. 


265 


neither  the  frequency  nor  the  extent  ?  Again,  does  not  the  bird 
advance  in  its  onward  course  with  variable  rapidity  ?  Shall 
we  not  find  in  the  action  of  its  wings  a  series  of  impulses, 
which  give  to  its  advancing  course  a  jerking  motion  ? 

These  queries  can  be  answered  experimentally  in  the  follow- 
ing manner. 

Since  we  have  at  our  disposal  the  means  of  sending  the 
signals  of  movements  to  a  distance,  and  recording  them  by 
tracings,  when  these  movements  are  made  to  produce  a  pres- 
sure on  the  membrane  of  a  drum  filled  with  air,  we  must 
endeavour  to  reduce  to  a  pressure  of  this  kind  the  movements 
which  we  desire  to  study. 

The  oscillations  which  can  be  effected  by  the  bird  in  a  hori- 
zontal plane  must  be  made  to  exert  on  the  membrane  of  the 
drum  pressures  alternately  strong  or  feeble,  in  proportion  as  the 
bird  mounts  or  descends.  The  same  kind  of  experiment  must 
be  made  on  the  variations  in  its  horizontal  rapidity. 

The  question  has  been  ^already  solved  for  the  vertical 
re-actions,  by  means  of  the  apparatus  represented  in  fig.  28, 
when  we  were  treating  of  terrestrial  locomotion  ;  a  slight 
modification  will  allow  us  to  employ  the  same  method  to 
ascertain  whether  vertical  oscillations  are  produced  during 
flight. 


F  io.  112.— Apparatus  intended  to  transmit  to  the  registering  instrument  all 
tne  vertical  oscillations  of  the  bird. 

Fig.  112  shows  the  arrangement  that  we  have  adopted. 
The  mass  of  lead  is  applied  directly  to  the  membrane ;  some 
wire- work  protects  the  upper  surface  of  the  apparatus  from 
the  friction  of  the  feathers  of  the  bird,  which,  without  this 
precaution,  might  sometimes  affect  the  form  of  the  tracing. 


*3 


RE-ACTIONS  DURING  FLIGHT. 


267 


After  having  convinced  ourselves  that  the  apparatus  trans- 
mits faithfully  the  movements  which  are  communicated  to  it, 
we  connect  it  with  the  registering  instrument  by  means  of  a 
long  tube,  and  place  it  on  the  back  of  a  bird,  which  is  then 
allowed  to  fly.  Experiments  made  on  many  different  species, 
pigeons,  wild  ducks,  buzzards,  moor-buzzards,  screech  owls, 
have  shown  that  there  are  very  varied  types  of  flight  with 
respect  to  the  intensity  of  the  oscillations  in  the  vertical 
plane. 

Fig.  113  shows  the  tracings  furnished  by  different  species 
of  birds.  All  these  tracings,  collected  on  a  cylinder  revolving 
with  a  constant  rapidity,  mid  referred  to  a  chronographic 
tuning-fork  vibrating  60  times  in  a  second,  enable  us  to 
ascertain  the  absolute  and  relative  duration  of  the  oscillations 
during  the  flight  of  different  species  of  birds. 

We  find  from  this  figure,  that  the  frequency  and  amplitude 
of  the  vertical  oscillations  vary  much  according  to  the  species 
of  the  bird.  In  order  to  ascertain  the  cause  of  each  of  these 
movements  with  greater  accuracy,  let  us  register  at  the  same 
time  the  vertical  oscillations  of  the  bird,  and  the  action  of  the 
muscles  of  the  wing.  If  we  make  this  double  experiment  on 
two  birds  which  differ  much  in  their  manner  of  flight,  such 
as  the  wild  duck  and  the  buzzard,  we  obtain  the  tracings 
represented  in  fig.  114. 

The  duck  (upper  line)  presents  at  each  elevation  of  its 
wing  two  energetic  oscillations ;  that  at  b,  at  the  moment  when 
the  wing  is  lowered,  is  easy  to  be  understood,  as  well  as  that 
at  a,  at  the  moment  that  the  wing  begins  to  rise  again.  To 
explain  the  ascent  of  the  bird  during  the  time  of  the  elevation 
of  the  wing,  it  seems  indispensable  to  refer  to  the  effect  of 
the  child's  kite,  to  which  we  have  before  alluded.  The  bird 
having  acquired  a  certain  velocity,  presents  its  wings  to  the 
air  as  inclined  planes;  an  effect  is  immediately  produced, 
similar  to  the  ascent  of  the  hovering  apparatus  which  trans- 
form their  acquired  velocity  into  ascensional  force.  The 
flight  of  the  buzzard  shows  also,  but  in  a  less  degree,  the 
ascent  which  accompanies  the  upward  movement  of  the 
wing. 

Determination  of  variations  in  the  rapidity  of  flight  — The 


268 


ANIMAL  MECHANISM. 


second  question  which  we  have  to  solve  relates  to  the  deter- 
mination of  the  various  phases  in  the  rapidity  of  flight.  It 
may  receive  its  solution  by  the  employment  of  the  same 
method.  If  the  drum,  loaded  with  a  piece  of  lead,  be  placed 
n  the  back  of  the  bird  so  as  to  present  its  membrane  in  a 
vertical  plane — that  is,  at  right  angles  to  the  direction  of  flight, 


<7 


Fig.  114. — In  the  upper  part  we  see,  placed  above  each  other,  the  muscular 
tracing  (see  p.  232),  and  that  of  the  vertical  oscillations  in  a  wild  duck. 
Under  the  undulation  a,  which  shows  the  elevation  of  the  wing,  is  seen  a 
vertical  oscillation ;  another  is  seen  under  6,  the  tracing  corresponding 
with  the  depression  of  the  wing.  In  the  lower  halt  of  the  figure  are 
tracings  collected  from  a  buzzard  ;  the  oscillation  at  »,  which  corresponds 
with  the  elevation  of  the  wing,  is  less  marked  than  that  from  the  duck. 

the  apparatus  would  be  insensible  to  vertical  oscillations,  and 
would  only  give  the  signal  of  those  which  are  made  backwards 
and  forwards.  Let  us  turn  the  membrane  of  the  drum  in 
front ;  it  is  evident  that  if  the  bird  quickens  its  speed,  the 
retarding  influence  of  the  inertia  of  the  mass  of  lead  will 
produce  a  pressure  on  the  membrane  of  the  drum ;  the  air 
will  be  compressed,  and  the  registering  lever  M  ill  rise ;  while 


RE-ACTIONS  DURING  FLIGHT.  269 


the  slackening  of  the  bird's  speed  will  cause  a  descent  of  the 
lever  by  an  inverse  action. 

Experiments  tried  upon  the  species  of  birds  before  men- 
tioned, have  furnished  us  with  tracings  analogous  with  those 
of  the  vertical  oscillations. 

If  it  be  true,  as  we  have  supposed,  that  the  vertical 
oscillation  of  the  bird,  at  the  moment  of  the  ascent  of  the 
wing,  is  due  to  the  transformation  of  speed  into  elevation, 
we  shall  have  the  means  of  verifying  this  supposition,  by 
collecting  simultaneously  the  tracings  of  the  vertical  oscilla- 
tions and  those  of  the  variations  of  rapidity. 

Thus,  by  registering  at  the  same  time  the  two  orders  of 
oscillation  in  the  flight  of  a  buzzard,  we  find  that  the  phase 
of  depression  of  the  wing  produces  at  the  same  time  the 
elevation  of  the  bird  and  the  acceleration  of  its  horizontal 
swiftness.  This  effect  is  the  natural  consequence  of  the 
inclination  of  the  plane  of  the  wing  at  the  moment  of  its 
descent ;  this  we  already  know  from  having  obtained  it  in  th.6 
flight  of  the  insect.  As  to  the  elevation  of  the  wing,  it  is 
found  that  during  the  slight  ascent  which  accompanies  it,  the 
swiftness  of  the  bird  diminishes.  In  fact,  the  curve  of  the 
variations  of  rapidity  is  depressed  at  the  moment  when  the 
bird  rises.  This  is,  therefore,  a  confirmation  of  the  theory 
which  we  have  propounded  coifterning  the  transformation  of 
the  horizontal  rapidity  of  the  bird  into  ascensional  force. 
Thus  by  this  mechanism,  the  stroke  of  the  descending  wing 
produces  the  force  which  will  cause  the  two  oscillations  of  the 
bird  in  the  vertical  plane.  It  produces  directly  the  ascent 
which  is  synchronous  with  it,  and  indirectly  prepares  the 
second  vertical  oscillation  of  the  bird  by  creating  rapidity. 

Simultaneous  tracing  of  the  two  orders  of  the  oscillations  of  the 
bird. — Instead  of  representing  separately  the  two  kinds  of 
oscillation  executed  by  the  bird  as  it  flies,  it  is  more  instruc- 
tive to  seek  to  obtain  a  single  curve  representing  together  the 
movements  which  the  body  of  the  bird  makes  as  it  advances 
in  space. 

The  method  which  we  have  employed  to  obtain  the  move- 
ments of  the  point  of  the  wing  may,  with  certain  modifica- 
tions, furnish  the  simultaneous  tracing  of  the  two  orders  of 
25  ' 


270 


ANIMAL  MECHANISM. 


movement  which  we  wish  to  investigate.  For  this  purpose,  the 
two  drums  combined  rectangularly  must  be  connected  with  the 
same  inert  mass. 

Let  us  refer  to  fig.  97  (p.  237),  where  we  see  the  two 
levers  connected  together  and  communicating  with  each  other 
by  tubes,  which  transmit  to  one  all  the  movements  executed 
by  the  other.  When  we  give  the  first  lever  any  kind  of 
movement,  we  see  it  reproduced  by  the  second  lever  in  the 
same  direction. 

Now,  let  each  of  these  levers  be  loaded  with  a  piece  of  lead, 
and  taking  in  our  hand  the  support  of  the  apparatus,  let  us 
cause  it  to  describe  any  kind  of  movement  in  a  plane  perpen- 
dicular to  the  direction  of  the  lever.  We  shall  see  that  the 
lever  No.  2  executes  movements  of  exactly  an  opposite  kind. 
In  fact,  since  the  motive  force  which  acts  on  the  membrane  of 
the  drums  is  nothing  more  than  the  inertia  of  the  mass  of 
lead,  and  the  movements  of  this  mass  are  always  later  than 
those  given  to  the  apparatus,  it  is  clear  that  if  we  raise 
the  whole  system,  the  mass  will  keep  the  lever  down,  while 
if  we  lower  the  instrument  the  mass  will  retain  the  lever 
above ;  that  if  we  carry  it  forward,  the  inertia  will  keep  the 
lever  back,  &c.  Therefore,  the  lever  No.  2,  only  going 
through  the  same  movements  as  No.  1,  will  give  curves  which 
will  be  absolutely  opposed  to"1;he  movement  which  has  been 
given  to  the  stand  of  the  apparatus.  This  being  assumed,  let 
us  pass  to  the  experiment;  for  this,  let  us  employ  the 
apparatus  represented  in  fig.  99  on  the  back  of  the  buzzard 
as  it  flies  ;  let  us  remove  the  rod  which  received  the  movements 
of  the  wing,  as  well  as  the  parallelogram  which  transmitted 
them  to  the  lever ;  we  will  only  retain  the  lever  fastened  to 
the  two  drums,  and  the  contrivance  which  fixes  the  whole 
instrument  on  the  back  of  the  buzzard ;  lastly,  let  us  adapt  a 
piece  of  lead  to  this  lever,  and  let  the  bird  fly.  The  tracing 
procured  is  represented  in  fig.  115.  The  analysis  of  this 
curve  is  at  first  sight  extremely  difficult ;  we  hope,  however, 
to  succeed  in  showing  its  signification. 

Analysis  of  the  curve  illustrating  the  oscillations  of  the  bird. — 
This  curve  is  described  on  the  cylinder  in  the  same  manner  as 
in  fig.  100,  which  shows  the  different  movements  of  the  point 


RE-ACTIONS  DURING  FLIGHT. 


27 


of  the  wing  ;  the  glass 
plate  moves  from  right  to 
left;  the  tracing  must  be 
read  from  left  to  right. 
The  head  of  the  bird  is 
turned  towards  the  left, 
its  'flight  is  in  the  direction 
pointed  out  by  the  arrow. 

We  may  divide  this 
figure  into  a  series  of 
portions  by  means  of  ver- 
tical lines  passing  through 
homologous  points,  whe- 
ther we  let  fall  these  per- 
pendiculars from  the  top 
of  the  loops,  or  from  that 
of  the  simple  curves,  as 
has  been  done  at  the  points 
a  and  e.  Each  of  these 
portions  will  enclose  toler- 
ably similar  elements,  with 
the  exception  of  their  un- 
equal development  in  the 
different  points  of  the 
figure :  let  us  neglect  this 
detail  for  the  present. 

It  is  evident  that  the 
periodical  return  of  similar 
forms  corresponds  with  the 
return  of  the  same  phases 
in  a  revolution  of  the  bird's 
wing.  The  portion  a  e  will, 
therefore,  represent  the  dif- 
ferent movements  of  the 
bird  in  one  and  the  same 
revolution. 

Let  us  remember  that  in 
the  curve  which  we  analyse, 
all  the  movements  are  con- 
trary to  those  really  per- 
formed by  the  bird.  The 


272 


ANIMAL  MECHANISM. 


two  vertical  oscillations  of  the  bird,  the  greater  and  the 
less,  must  thus  be  represented  by  two  curves,  of  which 
the  summit  will  be  placed  downwards.  It  is  easy  to  recognise 
their  existence  in  the  large  curve,  a  b  c,  and  the  smaller  one 
c  d  e.  The  bird  was,  therefore,  rising  from  a  to  b,  descending 
from  b  to  c ;  it  rose  again  from  c  to  d,  and  descended  from 
d  to  e. 

But  these  two  oscillations  encroach  on  each  other,  which 
produces  the  loop  c  d  ;  the  oscillation  c  d  e  partly  covers  the 
first  by  turning  towards  the  head  of  the  bird.  Since  the 
indications  of  the  curve  are  in  a  direction  contrary  to  the  real 
motion,  this  is  a  proof  that  the  bird,  at  this  moment,  was 
either  carried  backwards,  or  at  least  slackened  the  rapidity  of 
its  flight. 

This  figure,  therefore,  recalls  all  that  the  former  experiments 
have  taught  us  concerning  the  movements  of  the  bird  in 
space.  We  see  from  them,  that  at  each  revolution  of  its  wing 
it  rises  twice,  followed  by  two  descents ;  that  these  oscillations 
are  unequal :  the  larger  one,  as  we  know,  corresponds  with  the 
lowering  of  the  wing,  the  smaller  one  with  its  elevation.  We 
see,  also,  that  the  ascent  of  the  bird,  while  the  wing  is  rising, 
is  accompanied  by  the  slackening  of  its  speed,  which  justifies 
the  theory  that  this  re-ascent  is  made  at  the  expense  of  the 
velocity  acquired  by  the  bird. 

But  this  is  not  all :  fig.  115  shows  us,  also,  that  the  move- 
ments of  the  bird  are  not  the  same  at  the  commencement  as 
at  the  end  of  its  flight.  We  have  already  seen  (figs.  95  and 
100)  that  the  strokes  of  the  wing  at  its  departure  are  more 
extended;  we  see  here  that  the  oscillations  produced  at  its 
departure  by  the  descent  of  the  wing  (shown  at  the  left  hand 
of  the  figure)  are  also  more  extended.  But  theory  enables  us 
to  foresee  that  the  oscillation  of  the  ascent  of  the  wing,  being 
produced  by  the  velocity  of  the  bird,  must  be  very  feeble  at 
the  commencement  of  its  flight,  when  the  bird  has,  as  yet,  but 
little  rapidity.  This  figure  shows  us  that  this  is  actually  the 
case,  and  that  at  the  beginning  of  the  flight,  the  second 
oscillation  of  the  wing  (that  which  forms  the  loop)  is  but 
slight. 

We  are  now,  therefore,  in  possession  of  the  principal 


THEORY  OF  FLIGHT. 


273 


notions  on  which  may  be  established  the  mechanical  theory  of 
flight. 

From  all  these  experiments  we  may  deduce    that  it  is 
during  the  descent  of  the  wing  that  the  bird  acquires  all  the 
^Jipf  pJ&°ti^J-0TCe  w^icjtjsustains  and  directs  it  in  space.  ° 

■>y'*1  Theory  of  the  'flight  of  the  bircf. — Ontliis  subject, 
JhdAsiX^  almost  all  those  that  belong  to  this  discussion,  nearly  every 
^t^X,  thing  has  been  already  said ;  so  that  we  must  not  expect  to 
find  an  entirely  new  theory  arise  from  the  experiments  which 
have  been  described.  In  the  wrorks  of  Borelli  we  find  the 
first  correct  idea  of'  the  mechanism  of  flight.  The  wing, 
says  this  writer,  acts  on  the  air  like  a  wedge.  Developing 
still  farther  the  thought  of  the  learned  Neapolitan  physiologist, 
we  should  now  say  that  the  wing  of  the  bird  acts  on  the  air 
after  the  manner  of  an  inclined  plane,  in  order  to  produce  a 
re-action  against  this  resistance  which  impels  the  body  of  the 
bird  upward  and  forward.  This  theory,  confirmed  by  Strauss- 
Durkheim,  has  been  completed  by  Liais,  who  noticed  the 
double  action  of  the  wing ;  first,  that  which  in  the  phase  of 
depression  of  this  organ,  raises  the  bird  and  gives  it  an  im- 
pulse in  a  forward  direction  ;  then,  the  action  of  the  ascending 
wing,  which  is  guided  in  the  same  manner  as  a  boy's  kite, 
and  sustains  the  body  of  the  bird  until  the  following  stroke 
of  the  wing. 

We  have  been  reproached  for  relying  on  a  theory  which 
had  its  origin  more  than  two  centuries  ago  ;  we  much  prefer 
an  old  truth  to  the  most  modern  error ;  therefore  we  must  be 
allowed  to  render  to  the  genius  of  Borelli  Jhe  justice  which 
is  due  to  him,  and  only  claim  for  ourselves  the  merit  of  having 
furnished  the  experimental  demonstration  of  a  truth  already 
suspected. 

But  the  theories  which  had  been  propounded  up  to  the 
present  time  neglected  many  important  parts  which  experi- 
ments reveal,  and  which  we  are  about  to  endeavour  to  bring 
clearly  forward. 

Thus,  the  manner  in  which  the  change  in  the  plane  of  the 
wing  is  effected  in  every  part  of  the  flight  was  necessary  to 
bo  known,  in  order  to   explain  the  re-actions  which  tend 


274 


ANIMAL  MECHANISM. 


always  to  sustain  the  body  of  the  bird,  sometimes  by  acceler- 
ating the  rapidity  of  its  flight,  sometimes  by  slackening  it.* 
Fig.  Ill  shows  this  change  of  plane. 

As  to  the  re- actions  to  which  the  body  of  the  bird  is  sub- 
jected, experiment  has  clearly  demonstrated  them  ;  it  has 
furnished  us  with  the  means  of  estimating  their  absolute  force 
We  have  seen  that  these  re-actions  differ  according  to  th 
species  of  bird  which  is  observed.  They  are  powerful  and 
sudden  in  birds  which  have  a  small  sugfae^of  wing-  longer 
and  more  gentle  in  birds  formed  for  hovering'pthe  re-action 
of  the  period  of  the  re-ascent  of  the  wing  disappears  almost 
entirely  in  the  latter  kind. 

If  we  could  compare  terrestrial  locomotion  with  the  flight 
of  birds,  and  assimilate  alternate  with  simultaneous  move- 
ments, we  might  find  certain  analogies  between  the  walk 
of  man  and  the  flight  of  the  bird.  In  both,  the  body  is 
urged  forward  by  an  intermittent  impulse ;  man,  like  the 
bird,  raises  himself  by  borrowing  the  necessary  work  from 
the  dynamic  energy  which  he  has  acquired  by  his  muscular 
efforts. 

As  to  the  estimation  of  the  work  expended  in  flight,  we 
must,  before  we  can  undertake  it,  have  a  perfect  knowledge 
of  the  resistance  which  the  air  presents  to  surfaces  of  every 
form,  inclined  at  different  angles,  and  possessing  varied  velo- 
cities.   We  only  know  as  yet  the  movements  of  the  wings ; 


*  We  ought  to  beg  the  reader  to  remark  that  the  inclinations  repre- 
sented in  fig.  Ill  are  referred  to  a  line  which  probably  is  not  horizontal 
during  flight.  In  fact,  this  line  does  not  correspond  with  the  axis  of  the 
body  of  the  bird,  for  it  was  suspended  in  the  apparatus  by  a  corset  placed 
behind  its  wings,  and  thus  had  its  centre  of  gravity  in  front  of  the  point 
of  suspension,  which  caused  its  beak  to  hang  slightly  down.  In  free 
flight,  on  the  contrary,  the  axis  of  the  bird  is  horizontal— or  rather  turned 
somewhat  upward.  Kestored  to  this  proper  position,  a  fresh  direction 
would  be  given  to  each  of  the  positions  of  the  wing  (fig.  Ill),  which 
would  alter  them  all  by  the  same  number  of  degrees.  Then,  probably, 
we  should  see  that  the  wing  always  presents  its  lower  surface  to  the  air, 
as  the  only  one  which  can  find  in  it  a  point  of  resistance.  This  supposi- 
tion requires  for  its  verification  some  fresh  experiments,  which  we  hope  to 
be  soon  able  to  make. 


THEORY  OF  FLIGHT. 


275 


the  resistance  which  they  meet  with  in  the  air  has  yet  to  be 
determined.  Our  experiments  on  this  subject  are  still  being 
pursued.  When  once  we  have  these  two  elements,  the  mea- 
sure of  work  will  be  obtained  from  the  resistance  which  is 
presented  to  the  wing  by  the  air  at  every  instant,  multiplied 
by  the  distance  passed  over.  This  will  give  us  the  measure 
of  work  brought  to  bear  upon  the  air. 

For  its  horizontal  advance  the  bird  will  be  obliged  only  to 
furnish  the  quantity  of  work  equivalent  to  the  resistance 
presented  by  the  air  in  front  of  it,  multiplied  by  the  distance 
passed  through.  A  part  of  this  resistance,  namely,  that 
which  is  applied  to  the  lower  surface  of  the  wing,  is  utilised 
to  sustain  the  bird,  by  the  kind  of  action  which  we  have  com- 
pared to  that  of  a  child's  kite. 

It  appears  that  this  action  is  of  primary  importance  in  the 
flight  of  the  bird.  In  fact,  among  the  researches  on  the 
resistance  of  the  air  there  is  one  which  we  owe  to  Mons.  de 
Louvrie,  which  seems  to  prove  that  if  the  wing  make  a  very 
small  angle  with  the  horizon,  nearly  all  the  work  obtained 
from  the  dynamic  energy  of  the  bird  is  employed  to  sustain 
it ;  according  to  this  writer,  an  angle  of  6°  30'  would  be  the 
most  favourable  to  the  utilisation  of  its  energy.  The  im- 
portant part  played  by  the  gliding  of  the  wing  upon  the  air 
seems  also  proved  by  the  shape  of  that  organ,  v  The  wing 
being  alternately  active  when  it  strikes  the  air,  and  passive 
when  it  glides  through  it,  is  not,  in  all  its  parts,  equally 
adapted  to  this  double  function. 

When  a  surface  strikes  the  air,  it  must  move  with  rapidity 
in  order  to  find  resistance.  Thus  the  wing,  turning  around 
the  point  by  which  it  is  attached  to  the  body,  shows  unequal 
and  gradually-increasing  velocity  in  different  points  according 
as  they  are  nearer  to  the  body,  so  that  being  almost  nothing 
at  the  point  of  attachment  of  the  wing,  the  velocity  will  be 
very  great  at  the  free  end. 

Let  us  imagine  the  wing  of  an  insect  as  large  at  the  base 
as  at  the  extremity ;  this  size  would  be  useless  in  the  part 
nearest  to  the  body,  for  the  wing,  at  this  point,  has  not  suffi- 
cient rapidity  to  strike  the  air  with  effect.  Thus  we  find,  in 
the  greater  part  of  insects,  the  wing  reduced  to  a  strong 


276 


ANIMAL  MECHANISM. 


nervure  towards  its  base.  The  membranous  part  commences 
only  at  the  point  where  rapidity  of  movement  begins  to  be 
of  some  use,  and  the  membrane  goes  on  increasing  in  breadth 
till  near  the  extremity  of  the  wing.  Such  is  (fig.  116)  the 
type  of  the  wing  essentially  active — that  is,  intended  only  to 
strike  the  air.    ^.^^Jly  d  luJ^<^**jf  k&vJ&' 


In  the  bird,  on  the  contrafy7"Tfoe  *bf  the  phases  of -the 
movement  of  the  wing  is,  to  a  certain  extent,  passive ;  that 
is  to  say,  it  receives  the  pressure  of  the  air  on  its  lower  sur- 
face, when  the  bird  is  projected  rapidly  forward  by  its 
acquired  velocity.  Under  these  conditions,  the  whole  bird 
being  carried  forward  into  space,  all  the  parts  of  the  wing 
are  moved  with  the  same  rapidity ;  the  regions  near  to  the 
body  are  as  useful  as  the  others  to  take  advantage  of  the 
notion  of  the  air  which  presses  on  them  as  on  a  kite.-*c 


Fig.  117.— Active  and  passive  parts  of  the  bird's  wing. 

Thus,  the  base  of  the  wing  in  the  bird,  far  from  being  re- 
duced, as  in  the  insect,  to  a  rigid  but  bare  rib,  is  very  wide, 
and  furnished  with  feathers  and  wing  coverts  which  constitute 
a  large  surface,  under  which  the  air  presses  with  force,  and 
in  a  manner  very  efficacious  to  sustain  the  bird.  Fig.  117 
gives  an  idea  of  the  arrangement  of  the  wing  of  the  bird,  at 
the  same  time  active  and  passive. 

The  inner  part,  deprived  of  sufficient   velocity,  may  be 


REPRODUCTION  OF  MECHANISM  OF  FLIGHT.  277 


considered,  while  it  is  being  lowered,  as  the  passive  part  of  the 
organ,  while  the  external  part,  that  which  strikes  the  air,  is 
the  active  portion. 

By  its  very  great  velocity,  the  point  of  the  wing  must  meet 
with  more  resistance  from  the  air  than  any  other  part  of  this 
organ ;  whence  the  extreme  rigidity  of  the  large  feathers  of 
which  it  is  formed. 

The  conditions  of  decreasing  rapidity  explain  the  flexibility 
which  becomes  greater  and  greater  in  the  feathers  of  those 
parts  of  the  wing  nearer  to  the  body,  and  at  last  the  great 
thinness  of  those  at  the  base  or  passive  part  of  the  wing. 

Let  us  add  that  the  effect  of  the  kite  must  be  produced  at 
the  base  of  the  wing,  even  while  the  point  strikes  the  air,  so 
that  the  bird,  as  soon  as  it  has  acquired  its  velocity,  would 
be  constantly  lightened  of  part  of  its  weight,  on  account  of 
this  inclined  plane. 

The  reproduction  of  the  mechanism  of  flight  now  occupies  the 
minds  of  many  experimenters,  and  we  hesitate  not  to  own 
that  we  have  been  sustained  in  this  laborious  analysis  of  the 
different  acts  in  the  flight  of  the  bird,  by  the  assured  hope  of 
being  able  to  imitate,  more  or  less  imperfectly,  this  admirable 
type  of  aerial  locomotion.  We  have  already  met  with  some 
success  in  our  attempts,  which  have  been  interrupted  during 
the  last  two  years. 

Winged  apparatus  has  been  seen  in  our  laboratory,  which 
when  adapted  to  the  frame-work  which  had  held  the  bird, 
gave  it  a  rather  rapid  rotation.  But  this  was  only  a  very 
imperfect  imitation,  which  we  hope  shortly  to  improve. 
Already  a  young  and  ingenious  experimentalist,  Mons. 
Alphonse  Penaud,  has  obtained  much  more  satisfactory  results 
in  this  direction.  The  problem  of  aerial  locomotion,  formerly 
considered  a  Utopian  scheme,  is  now  approached  in  a  truly 
scientific  manner. 

The  plan  of  the  experiments  to  be  made  is  all  traced  out  : 
they  will  consist  in  continually  comparing  the  artificial  instru- 
ments of  flight  with  the  real  bird,  by  submitting  them  both 
to  the  modes  of  analysis  which  we  have  described  at  such 
length ;  the  apparatus  will,  from  time  to  time,  be  modified 
till  it  is  made  to  imitate  these  movements  faithfully.  For 


278 


ANIMAL  MECHANISM. 


this  purpose  we  are  about  to  undertake  a  new  series  of  ex- 
periments; some  new  apparatus  is  being  constructed,  which 
will  soon  be  finished. 

We  hope  that  we  have  proved  to  the  reader  that  nothing 
is  impossible  in  the  analysis  of  the  movements  connected  with 
the  flight  of  the  bird :  he  will  no  doubt  be  willing  to  allow 
that  mechanism  can  always  reproduce  a  movement,  the  nature 
of  which  has  been  clearly  defined. 


INDEX. 


Action  and  reaction,  109 

Air,  resistance  of,  changes  plane  of 

insect's  wing,  197 
Aliment,  heating  power  of,  16 
Animal  motion,  27 
Animals,  high  temperature  of,  21 

—      warm  and  cold  blooded,  23 
Apophyses,  cause  of,  89 
Automatic  regulator  of  temperature, 

25 

B. 

Beclard's  experiments  on  heat  and 
work,  17 

Bernard  on  automatic  regulator  of 

temperature,  25 
Bertrand  on  birds'  muscles,  212 
Biped  diagonal,  definition  of,  154 
B:rds,  conformation  of,  216 

—  curves  in  wing  of,  210 

—  electrical    experiment  on 

flight  of,  231 

—  flight  of,  209 

—  hovering  of,  221 

—  large  pectoral  muscles  of,  21 1 

—  M.  de  Lucy  on,  222 

—  muscular  force  of,  213 

—  passades  of,  220 

—  rapidity  of  muscular  action 

in,  214 

—  ressource  of,  220 

—  sailing  flight  of,  221 

—  stable  equilibrium  of,  216 
Birds'  wings,  compared  to  screw,  211 

—  —    duration  of  elevation 

and  depression  of,  229 

—  —    stroke  of,  forward  and 

backward,  235 
Blood,  circulation  of,  67 


Bones,  change  in  through  age,  90 
Borelli  on  locomotion,  103 

—  birds'  muscles,  212 

—  flight  of  birds,  273 

—  horse,  161 

Buzzard,  muscular  force  of  wing  of, 
213 


C. 

Chronograph  described,  122 
Circulation  of  blood,  variations  in, 
26 

—  —     furrows  the 

bones,  87, 88 

Climbing,  106 
Club-foot,  96 
Creeping,  105 

Curnieu  on  Eclipse's  gallop,  167 


D. 

Darwin's  natural  selection,  79 
Darwinists,  suggestions  to,  84 
Davy  on  torpedo,  52 
Development  theory,  78 
Diptera,  manner  of  flight  of,  208 
Dromedary,  paces  of,  173 
Duges  on  movements  of  horse,  139 
Duhamel's  chronographic  tuning- 
fork,  44 

Duval,  representation  of  horse  by 
zootrope,  177 


E. 

Electric  fishes,  51 


280 


INDEX. 


Electricity,  animal,  49 

—  disappearance  when  te- 

tanized,  50 

—  Du  Bois  Reymond  on, 

50 

—  mechanical  work  substi- 

tuted for,  51 
D'Esterno  on  night  of  birds,  221 


F. 


Fibre,  striped  and  un striped,  28 

—  and  tendon,  69 

—  in  old  age  replaced  by  tendon, 

98 

Force,  what,  5 

—  all  can  be  reduced  to  motion,  8 

—  indestructible,  6,  13 

—  potential,  12,  14 
Flight,  see  Wing. 

—  of  buzzard,  261 

—  of  birds,  209 

—  of  pigeon,  255 

—  mechanism  of,  imitated,  277 

—  sailing,  of  birds,  221 

—  slight  waste  of  substance  in, 

213 

Frog,  signals,  32 

1 '  Function  makes  the  organ,' '  Guerin, 
84 


Gorilla,  skull  in  old  and  young,  90 
Guerin  on  club  foot,  97 

—  on  change  of  bones  through 

age,  90 

—  theory  of  function,  84 


H. 

Hartings  on  ratio  of  birds'  wings  to 

weight,  223,  224 
Heat,  animal,  19 

—  loss  of,  in  external  organs,  22 

—  mechanical  equivalent  of,  15 

—  unit  of,  13 

Helmholtz  on  contraction  of  muscles, 
46 


Helmholtz  on  lost  time  in  muscular 

action,  48 
Herdenheim's  experiments  on  heat 

and  work,  17 
Hirn  on  heat  and  work,  18 
Homology  of  muscles,  73 
Horse  not  projected  into  air,  156 

—  paces  of,  139 

—  power,  68 

—  transition  of  paces  of,  172 

—  various  authors  on,  145 

—  Vincent  and  Goiffon  on,  151 

—  zootrope  figures  of,  177 
Hovering  of  birds,  221 
Humerus,  curvatures  in  head  of,  92 

—      a  contorted  femur,  91 


India-rubber,  change  of  heat  into 
work  in,  39 


Joule  on  equivalence  of  force,  15 


K. 


Kaleidophone  rod,  tracing  of,  191 

—        —  with    wing  oi 
wasp,  193 
Kangaroo,  development  of  crural 
muscles  in,  71 


Lamarck's  development  theory,  77 
Latour  on  movement  of  bird's  wing, 
212 

Lavoisier's  theory  of  animal  heat,  20 
Levers  in  animal  skeleton,  65 
Liais  on  double  action  of  bird's 

wing,  273 
Life,  organic  acts  of,  28 

—  of  relation,  28 
Locomotion,  aerial,  180-277 

—  aquatic,  106 

—  terrestrial,  102 


INDEX. 


281 


Lost  time  in  muscle,  Helmholtz,  43 
Lucy,  M.  de,  on  wings  of  birds,  222 
Lungs,  not  seat  of  combustion,  23 


M. 

Marey's  myograph,  32 
Matteucci  on  torpedo,  52 
Mechanical  work,  estimation  of,  61 

—  —     forms  of,  60 
Mechanism  of  flight,  reproduced, 

277 

Modification  of  animals,  100 

—       of  men,  101 
Momentum,  divided  between  gun 

and  carriage,  110 
Moreau  on  torpedo,  53 
Motion,  all  force  reduced  to,  8 
—     alternate  in  living  motive 
powers,  66 
Motors,  living,  dynamic  energy  of,  68 
Movements,  see  Tracings 

caused  by  muscles  in 
insect's  wing,  11)6 

—  of  snail,  105 

—  of  wing  of  birds,  226 

—  —       insects,  195, 

197 

Muschelbroeck  on  torpedo,  52 
Muscles,  absorption  of,  from  disease, 
96 

—  adaptation  of,  to  function, 

95 

—  change  of,  by  age,  99 

—  —       by  experiment, 

101 

—  fatty  degeneration  of,  97 

—  harmony  between  form  and 

function  in,  77 

—  homology  of,  73 

—  in  jaw  of  carnivora,  90 

—  in  man  and  ape,  75 

—  large,  slight  contraction  of, 

62 

—  lateral  dilatation  of,  36 

—  long  and  short,  70 

—  mechanical  force  in,  39 

—  pectoral  in  birds,  72,  211 

—  penniform,  70 

—  use  of,  acquired  by  habit, 

26 


Muscles,  work  of,  47 
Muscular  current,  negative  varia- 
tion of,  50 

—  contraction,  tone  heard 

in,  46 

—  force  of  birds,  213 

—  —  of  tissue,  64 

—  shocks,  50,  51 

—  system,  variation  in,  94 

—  tissue,  specific  force  of, 

64 

—  wave,  35 

—  —  speed  of,  38 
Myograph,  explanation  of,  31 


K 

Nerve,  function  of,  41 
Nervous  agent,  speed  of,  42 

—  —    Du  Bois  Reymond 

on,  41 

—  centres   command  action 

without  the  influence  ot 
the  brain,  29 

—  tetanus,  45 
Notation  of  paces,  man,  134 

—  —    horse,  amble,  142 

—  —       —  gallop,165, 

168, etseq. 

—  —      —  trot,  144 

—  —       —     — irregu- 

lar, 156 

—  —       —  walk,  142, 

163 

—  —     synoptical  table 

of,  145 

—  rule,  175 


O. 

Oscillation  of  body,  113 
Oxidation  of  blood,  20 


P. 

Passades  of  birds,  220 
Penaud's  flight  instrument,  277 


INDEX. 


Pettigrew,  Dr.,  on  birds' wings,  210 
Piste,  definition  of,  152 

—  of  amble,  162 

—  of  slow  gallop,  167 

—  of  Eclipse's  gallop,  167 

—  of  trot,  157 

—  of  walking  pace,  162 

Wine  on  stable  equilibrium  of  birds, 
216 

R. 

Reactions  defined,  115 

—  instruments  to  show,  116 

—  of  movements  of  wing  of 

birds,  264 

—  of  walking  (man),  127 

—  of  leap,  ditto,  131 

—  of  gallop,  ditto,  131 

—  of  trot  of  horse,  153 

—  of  gallop,  ditto,  165,  171 
Regnault's  equivalent  of  heat,  15 
Ressource  of  birds,  220 
Reymond,  du  Bois,  on  muscular 

shocks,  50 
Rhythm  of  paces,  133 
Running  (man),  125 


S. 

Selection,  natural,  81 

Shoe,  experimental,  113 

Skeleton,  action  of  aneurism  on,  87 

—  variability  of,  85 

—  change  of  course  and  at- 

tachment of 
muscles,  89 

—  —    in,  transmitted 

to  descendants, 
94 

—  hollows  worn  by  tendons 

in,  86 

Snail,  movements  of,  105 
Stepeurves,  127 

—  of  horse's  trot,  153 

—  —      gallop,  165 

—  —      walk,  160 
Stimulus  of  necessity,  83 
Synthetic  reproduction  of  move- 
ments in  man,  137 

—  —    in  horse,  177 


T. 

Temperature  of  animals,  23 
Tetanus,  muscular,  45 

—  from  strychnine,  46 

—  heat  developed  in,  49 

—  Volta  and  Weber  on  ner- 

vous, 45 
Thermo-dynamics,  14 
Torpedo,  experiments  on,  52 

—      lost  time  in,  56 
Tracings,  see  Table  of  Illustrations. 

—  of  walking  pace  (man), 

115 

—  of  running  (man),  128 

—  of  gallop  (man;,  131 

■ —      of  hopping  (man),  132 

—  of  leaping  (man),  131 

—  of  movements  of  insect's 

wing,  190  et  seq. 

—  of  action  of  pectoral  mus- 

cles of  birds,  232 

—  of  flight  of  wild  duck,  buz- 

zard, &c,  266 

—  of  Wheatstone's  rod  with 

wing  of  wasp  attached, 
191 

—  of  humming-bird  moth, 

191 

—  compared  with  vibrations 

of  chronograph,  121 
Traction,  effects  of,  on  skeleton, 
89 

Trajectory  of  pubis,  119 

—  of  bird's  wing,  234-240 
Transitions  in  paces  of  horse,  174 


U. 

Unit  of  heat,  13 
—  of  work,  14 


V. 

Veratrine,  muscle  under,  35  , 
Villeneuve,  Dr.,  on  birds'  wings,  223 
Vincent  and  Goiffon  on  horse,  151 
Volta  and  Weber  on  nervous  te- 
tanus, 45 


INDEX. 


2S3 


W. 

Walking  (man),  111 

—      (horse),  142 
Wing  (bird's) 

—  action  downward  and  back- 

ward at  each  stroke,  235 

—  active  and  passive  parts  of, 

276 

—  ascent  of,  like  action  of  boy's 

kite,  273 

—  analogy  to  human  arm,  211 

—  at  each  revolution  of,  bird 

rises  twice,  272 

—  change  of  plaue   in,  244, 

257 

—  compared  to  screw,  211 

—  curves  in,  210 

—  depression  of,  elevates  and 

carries  forward  the  body, 
269 

—  descent  of,  gives  all  motive 

force,  273 

—  duration   of  elevation  and 

depression  of,  228 

—  frequency  of  strokes  of,  227 

—  Hartings  on,  223 

—  instrument  to  show  change 

in  plane  of,  258 

—  inclination  of,  changes  gra- 

dually, 263 

—  M.  de  Lucy  on,  222 

—  Louvrte,  M.  de,  on  angle  of 

piano  of  bird's_wing,  275 

—  movements  of,  226 

—  ratio  to  weight,  222,  225 


"Wing  (birds') — continued. 

—  re-action  of  movements  of, 

on  body,  264 

—  —       —   of  wild  duck, 

&c,  267 

—  trajectory  of  pigeon's,  255 
Wing  (insects') 

—  act  as  inclined  planes,  200 

—  artificial  representation  of, 

198 

—  causes  of  movement  of,  196 

—  changes  in  plane  of,  190-204 

—  figure  -of- 8  movement  of,  195 

—  flexible  membrane  of,  208 

—  flight  instrument,  illustrat- 

ing, 206 

—  frequency  of  movement  of, 

181-185 

—  moves  downward  and  for- 

ward, 197 

—  movements  of,  determined 

optically,  187 

—  propulsion  of,  from  below 

upward  and  forward,  204 

—  shape  of,  276 

—  structure  of,  196 

—  trajectory  of  (Dr.  Pettigrew), 

201 

Work,  mechanical,  60 

—  unit  of,  16 


Z. 

Zootrope,  137 

Zuckung,  shock  of  muscles,  30 


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